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Background and Aims Cold stress in rice (Oryza sativa) plants at the reproductive stage prevents normal anther development and causes pollen sterility. Tapetum hypertrophy in anthers has been associated with pollen sterility in response to cold at the booting stage. Here, we re-examined whether the relationships between anther abnormality and pollen sterility caused by cold stress at the booting stage in rice can be explained by a monovalent factor such as tapetum hypertrophy. Methods After exposing plants to a 4-d cold treatment at the booting stage, we collected and processed anthers for transverse sectioning immediately and at the flowering stage. We anatomically evaluated the effect of cold treatment on anther internal morphologies, pollen fertilities and pollen numbers in the 13 cultivars with various cold sensitivities. Key Results We observed four types of morphological anther abnormalities at each stage. Pollen sterility was positively correlated with the frequency of undeveloped locules, but not with tapetum hypertrophy as commonly believed. In cold-sensitive cultivars grown at low temperatures, pollen sterility was more frequent than anther morphological abnormalities, and some lines showed remarkably high pollen sterility without any anther morphological alterations. Most morphological anomalies occurred only in specific areas within large and small locules. Anther length tended to shorten in response to cold treatment and was positively correlated with pollen number. One cultivar showed a considerably reduced pollen number, but fertile pollen grains under cold stress. We propose three possible relationships to explain anther structure and pollen sterility and reduction due to cold stress. Conclusions The pollen sterility caused by cold stress at the booting stage was correlated with the frequency of entire locule-related abnormalities, which might represent a phenotypic consequence, but not a direct cause of pollen abortion. Multivalent factors might underlie the complicated relationships between anther abnormality and pollen sterility in rice. [ABSTRACT FROM AUTHOR]

Selecting an appropriate target gene is critical to the success of oral RNA interference-based pest control. The selection of target genes has depended on their ability to induce lethality. However, the induction of lethality by oral RNAi is slow-acting, and crop damage can progress during this time. Here, we show that oral RNAi of the death-associated inhibitor of apoptosis protein 1 (diap1), unlike two conventional target genes, induces acute feeding cessation in the solanaceous pest, Henosepilachna vigintioctopunctata within 24 h. We also found that our designed dsRNA has high specificity and does not cause death or reduce diap1 expression in two non-target insects. Our results suggest that diap1 is an appropriate target in the context of the rapid reduction of crop damage. We propose that the phenotype of acute feeding cessation should be used as a novel criterion for selecting target genes for RNAi-based pest control. [ABSTRACT FROM AUTHOR]

Using co-expression network analysis, we identified 123 transcription factors (TFs) as candidate secondary cell wall regulators in rice. To validate whether these TFs are associated with secondary cell wall formation, six TF genes belonging to the MYB, NAC or homeodomain-containing TF families were overexpressed or downregulated in rice. With the exception of OsMYB58/63-RNAi plants, all transgenic plants showed phenotypes possibly related to secondary cell wall alteration, such as dwarfism, narrow and dark green leaves, and also altered rice cinnamyl alcohol dehydrogenase 2 (OsCAD2) gene expression and lignin content. These results suggest that many of the 123 candidate secondary cell wall-regulating TFs are likely to function in secondary cell wall formation in rice. Further analyses were performed for the OsMYB55/61 and OsBLH6 TFs, the former being a TF in which the Arabidopsis ortholog is known to participate in lignin biosynthesis (AtMYB61) and the latter being one for which no previous involvement in cell wall formation has been reported even in Arabidopsis (BLH6). OsMYB55/61 and OsBLH6–GFP fusion proteins localized to the nucleus of onion epidermal cells. Moreover, expression of a reporter gene driven by the OsCAD2 promoter was enhanced in rice calli when OsMYB55/61 or OsBLH6 was transiently expressed, demonstrating that they function in secondary cell wall formation. These results show the validity of identifying potential secondary cell wall TFs in rice by the use of rice co-expression network analysis. [ABSTRACT FROM PUBLISHER]

Yellowing/chlorophyll breakdown is a prominent phenomenon in leaf senescence, and is associated with the degradation of chlorophyll - protein complexes. From a rice mutant population generated by ionizing radiation, we isolated nyc4-1, a stay-green mutant with a defect in chlorophyll breakdown during leaf senescence. Using gene mapping, nyc4-1 was found to be linked to two chromosomal regions. We extracted Os07g0558500 as a candidate for NYC4 via gene expression microarray analysis, and concluded from further evidence that disruption of the gene by a translocation-related event causes the nyc4 phenotype. Os07g0558500 is thought to be the ortholog of THF1 in Arabidopsis thaliana. The thf1 mutant leaves show variegation in a light intensity-dependent manner. Surprisingly, the Fv/ Fm value remained high in nyc4-1 during the dark incubation, suggesting that photosystem II retained its function. Western blot analysis revealed that, in nyc4-1, the PSII core subunits D1 and D2 were significantly retained during leaf senescence in comparison with wild-type and other non-functional stay-green mutants, including sgr-2, a mutant of the key regulator of chlorophyll degradation SGR. The role of NYC4 in degradation of chlorophyll and chlorophyll - protein complexes during leaf senescence is discussed. [ABSTRACT FROM AUTHOR]

Most aerial parts of the plant body are products of the continuous activity of the shoot apical meristem (SAM). Leaves are the major component of the aerial plant body, and their temporal and spatial distribution mainly determines shoot architecture. Here we report the identification of the rice gene PLASTOCHRON3 ( PLA3)/ GOLIATH ( GO) that regulates various developmental processes including the rate of leaf initiation (the plastochron). PLA3/ GO encodes a glutamate carboxypeptidase, which is thought to catabolize small acidic peptides and produce small signaling molecules. pla3 exhibits similar phenotypes to pla1 and pla2– a shortened plastochron, precocious leaf maturation and rachis branch-to-shoot conversion in the reproductive phase. However, in contrast to pla1 and pla2, pla3 showed pleiotropic phenotypes including enlarged embryo, seed vivipary, defects in SAM maintenance and aberrant leaf morphology. Consistent with these pleiotropic phenotypes, PLA3 is expressed in the whole plant body, and is involved in plant hormone homeostasis. Double mutant analysis revealed that PLA1, PLA2 and PLA3 are regulated independently but function redundantly. Our results suggest that PLA3 modulates various signaling pathways associated with a number of developmental processes. [ABSTRACT FROM AUTHOR]

The rice homeobox gene OSH15 (Oryza sativa homeobox) is a member of the knotted1-type homeobox gene family. We report here on the identification and characterization of a loss-of-function mutation in OSH15 from a library of retrotransposon-tagged lines of rice. Based on the phenotype and map position, we have identified three independent deletion alleles of the locus among conventional morphological mutants. All of these recessive mutations, which are considered to be null alleles, exhibit defects in internode elongation. Introduction of a 14 kbp genomic DNA fragment that includes all exons, introns and 5′- and 3′- flanking sequences of OSH15 complemented the defects in internode elongation, confirming that they were caused by the loss-of-function of OSH15. Internodes of the mutants had abnormal-shaped epidermal and hypo- dermal cells and showed an unusual arrangement of small vascular bundles. These mutations demonstrate a role for OSH15 in the development of rice internodes. This is the first evidence that the knotted1-type homeobox genes have roles other than shoot apical meristem formation and/or maintenance in plant development. [ABSTRACT FROM AUTHOR]