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Cryptochromes are blue light receptors that regulate various light responses in plants. Arabidopsis cryptochrome 1 (CRY1) and cryptochrome 2 (CRY2) mediate blue light inhibition of hypocotyl elongation and long-day (LD) promotion of floral initiation. It has been reported recently that two negative regulators of Arabidopsis cryptochromes, Blue light Inhibitors of Cryptochromes 1 and 2 (BIC1 and BIC2), inhibit cryptochrome function by blocking blue light-dependent cryptochrome dimerization. However, it remained unclear how cryptochromes regulate the BIC gene activity. Here we show that cryptochromes mediate light activation of transcription of the BIC genes, by suppressing the activity of CONSTITUTIVE PHOTOMORPHOGENIC 1 (COP1), resulting in activation of the transcription activator ELONGATED HYPOCOTYL 5 (HY5) that is associated with chromatins of the BIC promoters. These results demonstrate a CRY-BIC negative-feedback circuitry that regulates the activity of each other. Surprisingly, phytochromes also mediate light activation of BIC transcription, suggesting a novel photoreceptor co-action mechanism to sustain blue light sensitivity of plants under the broad spectra of solar radiation in nature.

SUMMARY: Arabidopsis possesses approximately 2000 transcription factors (TFs) in its genome. They play pivotal roles in various biological processes but analysis of their function has been hampered by the overlapping nature of their activities. To uncover clues to their function, we generated inducible TF lines using glucocorticoid receptor (GR) fusion techniques in Arabidopsis. These TF‐GR lines each express one of 1255 TFs as a fusion with the GR gene. An average 14 lines of T2 transgenic TF‐GR lines were generated for each TF to monitor their function. To evaluate these transcription lines, we induced the TF‐GR lines of phytochrome‐interacting factor 4, which controls photomorphogenesis, with synthetic glucocorticoid dexamethasone. These phytochrome‐interacting factor 4‐GR lines showed the phenotype described in a previous report. We performed screening of the other TF‐GR lines for TFs involved in light signaling under blue and far‐red light conditions and identified 13 novel TF candidates. Among these, we found two lines showing higher anthocyanin accumulation under light conditions and we examined the regulating genes. These results indicate that the TF‐GR lines can be used to dissect functionally redundant genes in plants and demonstrate that the TF‐GR line collection can be used as an effective tool for functional analysis of TFs. Significance Statement: We generated inducible transcription factor (TF) lines in Arabidopsis, TF‐glucocorticoid receptor (GR) lines, each expressing one of 1255 TFs as a fusion with the GR gene that affects transportation to the nucleus by application of an inducer, dexamethasone. After evaluating these lines by examination of phytochrome‐interacting factor 4, we performed screening for TFs involved in light signaling from the TF‐GR lines and analyzed two that showed higher anthocyanin accumulation under light conditions. [ABSTRACT FROM AUTHOR]

SUMMARY: In gene‐trap screening of plant genomes, promoterless reporter constructs are often expressed without trapping of annotated gene promoters. The molecular basis of this phenomenon, which has been interpreted as the trapping of cryptic promoters, is poorly understood. Here, we found that cryptic promoter activation occurs by at least two different mechanisms using Arabidopsis gene‐trap lines in which a firefly luciferase (LUC) open reading frame (ORF) without an apparent promoter sequence was expressed from intergenic regions: one mechanism is 'cryptic promoter capturing', in which the LUC ORF captured pre‐existing promoter‐like chromatin marked by H3K4me3 and H2A.Z, and the other is 'promoter de novo origination', in which the promoter chromatin was newly formed near the 5′ end of the inserted LUC ORF. The latter finding raises a question as to how the inserted LUC ORF sequence is involved in this phenomenon. To examine this, we performed a model experiment with chimeric LUC genes in transgenic plants. Using Arabidopsis psaH1 promoter–LUC constructs, we found that the functional core promoter region, where transcription start sites (TSSs) occur, cannot simply be determined by the upstream nor core promoter sequences; rather, its positioning proximal to the inserted LUC ORF sequence was more critical. This result suggests that the insertion of the coding sequence alters the local distribution of TSSs in the plant genome. The possible impact of the two types of cryptic promoter activation mechanisms on plant genome evolution and endosymbiotic gene transfer is discussed. Significance Statement: In promoter‐trap screenings of plant genomes, unexplainable expression of the reporter is occasionally reported. This is hypothesized to be caused by the trapping of enigmatic cryptic promoters. Here we demonstrate that two types of cryptic promoters exist in terms of chromatin remodeling: one is the pre‐existing promoter‐like chromatin whose inherent transcripts are hardly detectable, and the other is the de novo origination of promoter chromatin accompanying reporter insertion. [ABSTRACT FROM AUTHOR]

SUMMARY: In Arabidopsis, stamen elongation, which ensures male fertility, is controlled by the auxin response factor ARF8, which regulates the expression of the auxin repressor IAA19. Here, we uncover a role for light in controlling stamen elongation. By an extensive genetic and molecular analysis we show that the repressor of light signaling COP1, through its targets HY5 and HYH, controls stamen elongation, and that HY5 – oppositely to ARF8 – directly represses the expression of IAA19 in stamens. In addition, we show that in closed flower buds, when light is shielded by sepals and petals, the blue light receptors CRY1/CRY2 repress stamen elongation. Coherently, at flower disclosure and in subsequent stages, stamen elongation is repressed by the red and far‐red light receptors PHYA/PHYB. In conclusion, different light qualities – sequentially perceived by specific photoreceptors – and the downstream COP1–HY5/HYH module finely tune auxin‐induced stamen elongation and thus male fertility. Significance Statement: In Arabidopsis auxin‐induced stamen elongation is essential for optimizing the transfer of pollen grains onto the pistil to allow successful fertilization. Here we show that different light qualities, via the conserved COP1–HY5/HYH module, finely tune auxin‐induced stamen elongation and thus male fertility. [ABSTRACT FROM AUTHOR]

Root hairs protruding from epidermal cells increase the surface area for water absorption and nutrient uptake. Various environmental factors including light, oxygen concentration, carbon dioxide concentration, calcium and mycorrhizal associations promote root hair formation in Arabidopsis thaliana. Light regulates the expression of a large number of genes at the transcriptional and post-transcriptional levels; however, there is little information linking the light response to root hair development. In this study, we describe a novel mutant, light-sensitive root-hair development 1 (lrh1), that displays enhanced root hair development in response to light. Hypocotyl and root elongation was inhibited in the lrh1 mutant, which had a late flowering phenotype. We identified the gene encoding the p14 protein, a putative component of the splicing factor 3b complex essential for pre-mRNA splicing, as being responsible for the lrh1 phenotype. Indeed, regulation of alternative splicing was affected in lrh1 mutants and treatment with a splicing inhibitor mimicked the lrh1 phenotype. Genome-wide alterations in pre-mRNA splicing patterns including differential splicing events of light signaling- and circadian clock-related genes were found in lrh1 as well as a difference in transcriptional regulation of multiple genes including upregulation of essential genes for root hair development. These results suggest that pre-mRNA splicing is the key mechanism regulating root hair development in response to light signals. [ABSTRACT FROM AUTHOR]

The CSN is a multiprotein complex required for proper plant development. Here, we show the isolation of a new plant-specific CSN-interacting F-box protein, denominated CFK1, that is regulated by the CSN and promotes hypocotyl elongation.The regulation of protein turnover by the ubiquitin proteasome system (UPS) is a major posttranslational mechanism in eukaryotes. One of the key components of the UPS, the COP9 signalosome (CSN), regulates ‘cullin–ring’ E3 ubiquitin ligases. In plants, CSN participates in diverse cellular and developmental processes, ranging from light signaling to cell cycle control. In this work, we isolated a new plant-specific CSN-interacting F-box protein, which we denominated CFK1 (COP9 INTERACTING F-BOX KELCH 1). We show that, in Arabidopsis thaliana, CFK1 is a component of a functional ubiquitin ligase complex. We also show that CFK1 stability is regulated by CSN and by proteasome-dependent proteolysis, and that light induces accumulation of the CFK1 transcript in the hypocotyl. Analysis of CFK1 knockdown, mutant, and overexpressing seedlings indicates that CFK1 promotes hypocotyl elongation by increasing cell size. Reduction of CSN levels enhances the short hypocotyl phenotype of CFK1-depleted seedlings, while complete loss of CSN activity suppresses the long-hypocotyl phenotype of CFK1-overexpressing seedlings. We propose that CFK1 (and its regulation by CSN) is a novel component of the cellular mechanisms controlling hypocotyl elongation. [ABSTRACT FROM AUTHOR]

It is likely that many small ORFs (sORFs; 30-100 amino acids) are missed when genomes are annotated. To overcome this limitation, we identified ~8,000 sORFs with high coding potential in intergenic regions of the Arabidopsis thaliana genome. However, the question remains as to whether these coding sORFs play func- tional roles. Using a designed array, we generated an expression atlas for 16 organs and 17 environmental conditions among 7,901 identified coding sORFs. A total of 2,099 coding sORFs were highly expressed under at least one experimental condition, and 571 were significantly conserved in other land plants. A total of 473 coding sORFs were overexpressed; ~10% (49/473) induced visible pheno- typic effects, a proportion that is approximately seven times higher than that of randomly chosen known genes. These results indicate that many coding sOREs hidden in plant genomes are associated with morphogenesis. We believe that the expression atlas will contribute to further study of the roles of sOREs in plants. [ABSTRACT FROM AUTHOR]

Hydrangea (Hydrangea macrophylla) is tolerant of acidic soils in which toxicity generally arises from the presence of the soluble aluminum (Al) ion. When hydrangea is cultivated in acidic soil, its resulting blue sepal color is caused by the Al complex formation of anthocyanin. The concentration of vacuolar Al in blue sepal cells can reach levels in excess of approximately 15 mM, suggesting the existence of an Al-transport and/or storage system. However, until now, no Al transporter has been identified in Al hyperaccumulating plants, animals or microorganisms. To identify the transporter being responsible for Al hyperaccumulation, we prepared a cDNA library from blue sepals according to the sepal maturation stage, and then selected candidate genes using a microarray analysis and an in silico study. Here, we identified the vacuolar and plasma membrane-localized Al transporters genes vacuolar Al transporter (VALT) and plasma membrane Al transporter 1 (PALT1), respectively, which are both members of the aquaporin family. The localization of each protein was confirmed by the transient co-expression of the genes. Reverse transcription-PCR and immunoblotting results indicated that VALT and PALT1 are highly expressed in sepal tissue. The overexpression of VALT and PALT1 in Arabidopsis thaliana conferred Altolerance and Al-sensitivity, respectively. [ABSTRACT FROM AUTHOR]

Phytochrome is a red (R)/far-red (FR) light–sensing photoreceptor that regulates various aspects of plant development. Among the members of the phytochrome family, phytochrome A (phyA) exclusively mediates atypical phytochrome responses, such as the FR high irradiance response (FR-HIR), which is elicited under prolonged FR. A proteasome-based degradation pathway rapidly eliminates active Pfr (the FR -absorbing form of phyA) under R. To elucidate the structural basis for the phyA-specific properties, we systematically constructed 16 chimeric phytochromes in which each of four parts of the phytochrome molecule, namely, the N-terminal extension plus the Per/Arnt/Sim domain (N-PAS), the cGMP phosphodiesterase/adenyl cyclase/FhlA domain (GAF), the phytochrome domain (PHY), and the entire C-terminal half, was occupied by either the phyA or phytochrome B sequence. These phytochromes were expressed in transgenic Arabidopsis thaliana to examine their physiological activities. Consequently, the phyA N-PAS sequence was shown to be necessary and sufficient to promote nuclear accumulation under FR , whereas the phyA sequence in PHY was additionally required to exhibit FR-HIR. Furthermore, the phyA sequence in PHY alone substantially increased the light sensitivity to R. In addition, the GAF phyA sequence was important for rapid Pfr degradation. In summary, distinct structural modules, each of which confers different properties to phyA, are assembled on the phyA molecule. [ABSTRACT FROM AUTHOR]

It is poorly understood how plants control their growth by cell division, elongation, and differentiation. We have characterized a seedling-lethal mutant segregation distortion 3 (sd3) that showed a very dwarf phenotype when grown in the light and, in the dark, had short hypocotyls with reduced ploidy levels. The corresponding gene of SD3 encodes a protein with high similarity to yeast translocase on the inner mitochondrial membrane 21 (TIM21), which is a component of the TIM23 complex. Indeed, SD3 protein fused to GFP localized in the mitochondria. SD3 overexpression increased cotyledon size in the light and hypocotyl thickness in the dark. The expression of genes for several subunits of the respiratory-chain complexes III and IV was up-regulated in SD3-overexpressing plants. Furthermore, these plants showed high levels of ATP whereas those of sd3 were low. These results suggested that SD3 induced an increase in cell size by raising the expression of the respiratory-chain subunit genes and hence increased the intracellular ATP levels. We propose that intracellular ATP levels regulated by mitochondria control plant organ size. [ABSTRACT FROM PUBLISHER]

The strong regulation of plant carbon allocation and growth by trehalose metabolism is important for our understanding of the mechanisms that determine growth and yield, with obvious applications in crop improvement. To gain further insight on the growth arrest by trehalose feeding, we first established that starch-deficient seedlings of the ptastidic phosphoglucomutase1 mutant were similarly affected as the wild type on trehalose. Starch accumulation in the source cotyledons, therefore, did not cause starvation and consequent growth arrest in the growing zones. We then screened the FOX collection of Arabidopsis (Arabidopsis thaliana) expressing full-length cDNAs for seedling resistance to 100 mM trehalose. Three independent transgenic lines were identified with dominant segregation of the trehalose resistance trait that overexpress the bZIP11 (for basic region/leucine zipper motif) transcription factor. The resistance of these lines to trehalose could not be explained simply through enhanced trehalase activity or through inhibition of bZIP11 translation. Instead, trehalose-6-phosphate (T6P) accumulation was much increased in bZIP11-overexpressing lines, suggesting that these lines may be insensitive to the effects of T6P. T6P is known to inhibit the central stress-integrating kinase SnRK1 (KIN10) activity. We confirmed that this holds true in extracts from seedlings grown on trehalose, then showed that two independent transgenic lines overexpressing KIN10 were insensitive to trehalose. Moreover, the expression of marker genes known to be jointly controlled by SnRK1 activity and bZIPll was consistent with low SnRK1 or bZIP11 activity in seedlings on trehalose. These results reveal an astonishing case of primary metabolite control over growth by way of the SnRK1 signaling pathway involving T6P, SnRK1, and bZIPll. [ABSTRACT FROM AUTHOR]

Summary [ABSTRACT FROM AUTHOR]

Environmental stresses are major factors in limiting plant growth and crop production. To find genes improving salt tolerance, the screening of a large population of transgenic Arabidopsis thaliana that expressed rice full-length cDNAs under salinity stress is reported here. In this study one of the isolated salt-tolerant lines, R07303 was analysed in detail. An uncharacterized rice gene CHLOROPLAST PROTEIN-ENHANCING STRESS TOLERANCE (OsCEST) was integrated in R07303. Newly constructed transgenic Arabidopsis that overexpressed OsCEST or its Arabidopsis homologue AtCEST showed improved tolerance to salinity stress. OsCEST and AtCEST were mainly transcribed in photosynthetic tissues. Green fluorescent protein-fused OsCEST and AtCEST proteins were localized to the chloroplast in the Arabidopsis leaf protoplasts. CEST-overexpressing Arabidopsis showed enhanced tolerance not only to salt stress but also to drought stress, high-temperature stress, and paraquat, which causes photooxidative stress. Under saline conditions, overexpression of CESTs modulated the stress-induced impairment of photosynthetic activity and the peroxidation of lipids. Reduced expression of AtCEST because of double-stranded RNA interference resulted in the impairment of photosynthetic activity, the reduction of green pigment, defects in chloroplast development, and growth retardation under light. This paper discusses the relationship between the chloroplast protein CEST and photooxidative damage. [ABSTRACT FROM PUBLISHER]

Yeast one-hybrid screening is widely used for the identification of transcription factors (TFs) that interact with specific DNA sequences. However, screening a whole cDNA library is not efficient for the identification of TFs because TF genes represent only a small percentage of clones in a cDNA library. Here, we present the development of an efficient yeast one-hybrid screening system using a prey library composed only of approximately 1,500 TF cDNAs of Arabidopsis thaliana. This library enabled us to isolate a TF that binds to a specific promoter sequence with high efficiency, even when the promoter region of the gene of interest was directly employed as bait. Furthermore, this library was also successfully applied as a yeast two-hybrid library to find TFs that interact with specific proteins. This efficient system will contribute to the elucidation of gene regulatory networks in plants. [ABSTRACT FROM AUTHOR]

Background: Reminiscent of their free-living cyanobacterial ancestor, chloroplasts proliferate by division coupled with the partition of nucleoids (DNA-protein complexes). Division of the chloroplast envelope membrane is performed by constriction of the ring structures at the division site. During division, nucleoids also change their shape and are distributed essentially equally to the daughter chloroplasts. Although several components of the envelope division machinery have been identified and characterized, little is known about the molecular components/mechanisms underlying the change of the nucleoid structure. Results: In order to identify new factors that are involved in the chloroplast division, we isolated Arabidopsis thaliana chloroplast division mutants from a pool of random cDNA-overexpressed lines. We found that the overexpression of a previously uncharacterized gene (AtYLMG1-1) of cyanobacterial origin results in the formation of an irregular network of chloroplast nucleoids, along with a defect in chloroplast division. In contrast, knockdown of AtYLMG1-1 resulted in a concentration of the nucleoids into a few large structures, but did not affect chloroplast division. Immunofluorescence microscopy showed that AtYLMG1-1 localizes in small puncta on thylakoid membranes, to which a subset of nucleoids colocalize. In addition, in the cyanobacterium Synechococcus elongates, overexpression and deletion of ylmG also displayed defects in nucleoid structure and cell division. Conclusions: These results suggest that the proper distribution of nucleoids requires the YlmG protein, and the mechanism is conserved between cyanobacteria and chloroplasts. Given that ylmG exists in a cell division gene cluster downstream of ftsZ in gram-positive bacteria and that ylmG overexpression impaired the chloroplast division, the nucleoid partitioning by YlmG might be related to chloroplast and cyanobacterial division processes. [ABSTRACT FROM AUTHOR]

Leaf trichomes in Arabidopsis thaliana develop through several distinct cellular processes, such as patterning, differentiation, and growth. Although recent studies have identified several key transcription factors as regulating early patterning and differentiation steps, it is still largely unknown how these regulatory proteins mediate subsequent trichome development, which is accompanied by rapid cell growth and branching. Here, we report a novel trichome mutation in Arabidopsis, which in contrast with previously identified mutants, increases trichome cell size without altering its overall patterning or branching. We show that the corresponding gene encodes a GT-2-LIKE1 (GTL1) protein, a member of the trihelix transcription factor family. GTL1 is present within the nucleus during the postbranching stages of trichome development, and its loss of function leads to an increase in the nuclear DNA content only in trichomes that have completed branching. Our data further demonstrate that the gtl1 mutation modifies the expression of several cell cycle genes and partially rescues the ploidy defects in the cyclin-dependent kinase inhibitor mutant siamese. Taken together, this study provides the genetic evidence for the requirement of transcriptional regulation in the repression of ploidy-dependent plant cell growth as well as for an involvement of GTL trihelix proteins in this regulation. [ABSTRACT FROM AUTHOR]

In most algae, the chloroplast division rate is held constant to maintain the proper number of chloroplasts per cell. By contrast, land plants evolved cell and chloroplast differentiation systems in which the size and number of chloroplasts change along with their respective cellular function by regulation of the division rate. Here, we show that PLASTID DIVISION (PDV) proteins, land plant-specific components of the division apparatus, determine the rate of chloroplast division. Overexpression of PDV proteins in the angiosperm Arabidopsis thaliana and the moss Physcomitrella patens increased the number but decreased the size of chloroplasts; reduction of PDV levels resulted in the opposite effect. The level of PDV proteins, but not other division components, decreased during leaf development, during which the chloroplast division rate also decreased. Exogenous cytokinins or overexpression of the cytokinin-responsive transcription factor CYTOKININ RESPONSE FACTOR2 increased the chloroplast division rate, where PDV proteins, but not other components of the division apparatus, were upregulated. These results suggest that the integration of PDV proteins into the division machinery enabled land plant cells to change chloroplast size and number in accord with the fate of cell differentiation. [ABSTRACT FROM AUTHOR]

Quantitative morphological traits may be defined based on the 3D anatomy reconstructed from micro X-ray computed tomography (μCT) images. In this study, the heterogeneous spatial distribution of trichomes (hairs) on the adaxial leaf blade surface in Arabidopsis was evaluated in terms of 3D quantitative traits, including trichome number, average nearest-neighbour distance between trichomes, and proportion of large trichomes. The data reflect spatial heterogeneity in the radial direction, in that a greater number of trichomes were observed on the leaf blade margins relative to the non-margins, a distribution effect caused by the CAPRICE ( CPC) and GLABRA3 ( GL3) genes, which have previously been shown to affect trichome density. We further determined that the proportion of large trichomes on the blade mid-rib increases from the proximal end to the distal leaf tip in both wild-type plants and GL3 mutants. Our results indicate that the GL3 gene affects trichome distribution, rather than trichome growth, causing trichome initiation at the proximal base rather than the distal tip. On the other hand, CPC does affect trichome growth and developmental progression. Hence, quantitative phenotyping based on μCT enables precise phenotypic description for elucidation of gene control in morphological mutants. [ABSTRACT FROM AUTHOR]

Background: Plant promoter architecture is important for understanding regulation and evolution of the promoters, but our current knowledge about plant promoter structure, especially with respect to the core promoter, is insufficient. Several promoter elements including TATA box, and several types of transcriptional regulatory elements have been found to show local distribution within promoters, and this feature has been successfully utilized for extraction of promoter constituents from human genome. Results: LDSS (Local Distribution of Short Sequences) profiles of short sequences along the plant promoter have been analyzed in silico, and hundreds of hexamer and octamer sequences have been identified as having localized distributions within promoters of Arabidopsis thaliana and rice. Based on their localization patterns, the identified sequences could be classified into three groups, pyrimidine patch (Y Patch), TATA box, and REG (Regulatory Element Group). Sequences of the TATA box group are consistent with the ones reported in previous studies. The REG group includes more than 200 sequences, and half of them correspond to known cis-elements. The other REG subgroups, together with about a hundred uncategorized sequences, are suggested to be novel cis-regulatory elements. Comparison of LDSS-positive sequences between Arabidopsis and rice has revealed moderate conservation of elements and common promoter architecture. In addition, a dimer motif named the YR Rule (C/T A/G) has been identified at the transcription start site (-1/+1). This rule also fits both Arabidopsis and rice promoters. Conclusion: LDSS was successfully applied to plant genomes and hundreds of putative promoter elements have been extracted as LDSS-positive octamers. Identified promoter architecture of monocot and dicot are well conserved, but there are moderate variations in the utilized sequences. [ABSTRACT FROM AUTHOR]

Endoreduplication is a type of cell cycle in which DNA replication continues without cell division. We have isolated several dominant mutants from Arabidopsis thaliana activation tagging lines by flow cytometry. One of the mutants, increased level of polyploidy1-1D (ilp1-1D), showed increased polyploidy in both light- and dark-grown hypocotyls. The corresponding gene of ilp1-1D encodes a protein homologous to the C-terminal region of mammalian GC binding factor. We demonstrate that this protein functions as a transcriptional repressor in vivo. The expression of all members of the CYCLINA2 (CYCA2) family was reduced in an ILP1 overexpressing line, and the mouse (Mus musculus) homolog of ILP1 repressed cyclin A2 expression in mouse NIH3T3 cells. T-DNA insertion mutants of ILP1 showed reduced polyploidy and upregulated all CYCA2 expression. Furthermore, loss of CYCA2;1 expression induces an increase in polyploidy in Arabidopsis. We demonstrate that this protein regulates endoreduplication through control of CYCA2 expression in Arabidopsis. [ABSTRACT FROM AUTHOR]

F-box proteins regulate diverse cellular processes, including cell cycle transition, transcriptional regulation and signal transduction, by playing roles in Skp1p-cullin-F-box protein (SCF) complexes or non-SCF complexes. F-box proteins are encoded by a large gene family. Our database search revealed that at least 568 F-box protein genes are present in the Arabidopsis thaliana (Arabidopsis) genome. Domain search analysis using SMART and Pfam-A databases revealed that 67 of the F-box proteins contained Kelch repeats and 29 contained leucine-rich repeats (LRRs). Interestingly only two F-box proteins contained WD40 repeats that are found in many F-box proteins of other organisms. Kelch repeats, LRRs and WD40 repeats are implicated in protein–protein interactions. This analysis also resulted in the finding of several unique functional domains; however, 448 of the F-box proteins did not contain any known domains. Therefore, these proteins were used to search the Pfam-B database to find novel domains, and three putative ones were found. These domain search analyses led us to classify the Arabidopsis F-box proteins into at least 19 groups based on their domain structures. Macro array analysis showed that several F-box protein genes are expressed in a tissue-specific manner. [ABSTRACT FROM PUBLISHER]

Analysis of genomic DNA of Arabidopsis Columbia (Col.) ecotype using a transposon Tag1-specific primer showed the presence of Tag1 homologues which was confirmed by Southern hybridization with a Tag1 probe. Further analysis showed that the homologue, 0.75 kb in length, had inverted repeats at both ends, 8-bp duplicated sequences at the site at which it is located and about 80% homology with Tag1, and was randomly distributed in the Arabidopsis genome. Based on these results, we concluded that these elements are non-autonomous variants of Tag1 and we termed this element sTag1. Using the polymerase chain reaction fragment hybridization technique, we found the distribution of such homologues in other plant species. [ABSTRACT FROM PUBLISHER]

Abstract: The water–water cycle is the electron flow through scavenging enzymes for the reactive species of oxygen in chloroplasts, and is proposed to play a role in alternative electron sink in photosynthesis. Here we showed that the water–water cycle is impaired in the T-DNA insertion mutant of AtHMA1 gene encoding a Cu transporting ATPase in chloroplasts. Chlorophyll fluorescence under steady state was not affected in hma1, indicating that photosynthetic electron transport under normal condition was not impaired. Under electron acceptor limited conditions, however, hma1 showed distinguished phenotype in chlorophyll fluorescence characteristics. The most severe phenotype of hma1 could be observed in high (0.1%) CO2 concentrations, indicating that hma1 has the defect other than photorespiration. The transient increase of chlorophyll fluorescence upon the cessation of the actinic light as well as the NPQ induction of chlorophyll fluorescence revealed that the two pathways of cyclic electron flow around PSI, NDH-pathway and FQR-pathway, are both intact in hma1. Based on the NPQ induction under 0% oxygen condition, we conclude that the water–water cycle is impaired in hma1, presumably due to the decreased level of Cu/Zn SOD in the mutant. Under high CO2 condition, hma1 exhibited slightly higher NPQ induction than wild type plants, while this increase of NPQ in hma1 was suppressed when hma1 was crossed with crr2 having a defect in NDH-mediated PSI cyclic electron flow. We propose that the water–water cycle and NDH-mediated pathways might be regulated compensationally with each other especially when photorespiration is suppressed. [Copyright &y& Elsevier]

Abstract: Recently, we developed a novel system known as Full-length cDNA Over-eXpressor (FOX) gene hunting [T. Ichikawa, M. Nakazawa, M. Kawashima, H. Iizumi, H. Kuroda, Y. Kondou, Y. Tsuhara, K. Suzuki, A. Ishikawa, M. Seki, M. Fujita, R. Motohashi, N. Nagata, T. Takagi, K. Shinozaki, M. Matsui, The FOX hunting system: an alternative gain-of-function gene hunting technique, Plant J. 48 (2006) 974–985], which involves the random overexpression of a normalized Arabidopsis full-length cDNA library. While our system allows large-scale collection of full-length cDNAs for gene discovery, we sought to downsize it to analyze a small pool of full-length cDNAs. As a model system, we focused on stress-inducible transcription factors. The full-length cDNAs of 43 stress-inducible transcription factors were mixed to create a transgenic plant library. We screened for salt-stress-resistant lines in the T1 generation and identified a number of salt-tolerant lines that harbored the same transgene (F39). F39 encodes a bZIP-type transcription factor that is identical to AtbZIP60, which is believed to be involved in the endoplasmic reticulum stress response. Microarray analysis revealed that a number of stress-inducible genes were up-regulated in the F39-overexpressing lines, suggesting that AtbZIP60 is involved in stress signal transduction. Thus, our mini-scale FOX system may be used to screen for genes with valuable functions, such as transcription factors, from a small pool of genes that show similar expression profiles. [Copyright &y& Elsevier]