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Shoot branching significantly influences yield and timber quality in woody plants, with hybrid Liriodendron being particularly valuable due to its rapid growth. However, understanding of the mechanisms governing shoot branching in hybrid Liriodendron remains limited. In this study, we systematically examined axillary bud development using morphological and anatomical approaches and selected four distinct developmental stages for an extensive transcriptome analysis. A total of 9,449 differentially expressed genes have been identified, many of which are involved in plant hormone signal transduction pathways. Additionally, we identified several transcription factors downregulated during early axillary bud development, including a noteworthy gene annotated as CYC-like from the TCP TF family, which emerged as a strong candidate for modulating axillary bud development. Quantitative real-time polymerase chain reaction results confirmed the highest expression levels of LhCYCL in hybrid Liriodendron axillary buds, while histochemical β-glucuronidase staining suggested its potential role in Arabidopsis thaliana leaf axil development. Ectopic expression of LhCYCL in A. thaliana led to an increase of branches and a decrease of plant height, accompanied by altered expression of genes involved in the plant hormone signaling pathways. This indicates the involvement of LhCYCL in regulating shoot branching through plant hormone signaling pathways. In summary, our results emphasize the pivotal role played by LhCYCL in shoot branching, offering insights into the function of the CYC-like gene and establishing a robust foundation for further investigations into the molecular mechanisms governing axillary bud development in hybrid Liriodendron.Key message: This study systematically observed the axillary bud development in hybrid Liriodendron and found that LhCYCL promotes shoot branching by precisely regulating the expression of plant hormone signaling pathway genes. [ABSTRACT FROM AUTHOR]

Key message: ‘Sikkim Primitive’ maize landrace, unique for prolificacy (7–9 ears per plant) possesses unique genomic architecture in branching and inflorescence-related gene(s), and locus Zm00001eb365210 encoding glycosyltransferases was identified as the putative candidate gene underlying QTL (qProl-SP-8.05) for prolificacy. The genotype possesses immense usage in breeding high-yielding baby-corn genotypes. ‘Sikkim Primitive’ is a native landrace of North Eastern Himalayas, and is characterized by having 7–9 ears per plant compared to 1–2 ears in normal maize. Though ‘Sikkim Primitive’ was identified in the 1960s, it has not been characterized at a whole-genome scale. Here, we sequenced the entire genome of an inbred (MGUSP101) derived from ‘Sikkim Primitive’ along with three non-prolific (HKI1128, UMI1200, and HKI1105) and three prolific (CM150Q, CM151Q and HKI323) inbreds. A total of 942,417 SNPs, 24,160 insertions, and 27,600 deletions were identified in ‘Sikkim Primitive’. The gene-specific functional mutations in ‘Sikkim Primitive’ were classified as 10,847 missense (54.36%), 402 non-sense (2.015%), and 8,705 silent (43.625%) mutations. The number of transitions and transversions specific to ‘Sikkim Primitive’ were 666,021 and 279,950, respectively. Among all base changes, (G to A) was the most frequent (215,772), while (C to G) was the rarest (22,520). Polygalacturonate 4-α-galacturonosyltransferase enzyme involved in pectin biosynthesis, cell-wall organization, nucleotide sugar, and amino-sugar metabolism was found to have unique alleles in ‘Sikkim Primitive’. The analysis further revealed the Zm00001eb365210 gene encoding glycosyltransferases as the putative candidate underlying QTL (qProl-SP-8.05) for prolificacy in ‘Sikkim Primitive’. High-impact nucleotide variations were found in ramosa3 (Zm00001eb327910) and zeaxanthin epoxidase1 (Zm00001eb081460) genes having a role in branching and inflorescence development in ‘Sikkim Primitive’. The information generated unraveled the genetic architecture and identified key genes/alleles unique to the ‘Sikkim Primitive’ genome. This is the first report of whole-genome characterization of the ‘Sikkim Primitive’ landrace unique for its high prolificacy. [ABSTRACT FROM AUTHOR]

The genus Striga, also called "witchweed", is a member of the family Orobanchaceae, which is a major family of root-parasitic plants. Striga can lead to the formation of seed stocks in the soil and to explosive expansion with enormous seed production and stability once the crops they parasitize are cultivated. Understanding the molecular mechanism underlying the communication between Striga and their host plants through natural seed germination stimulants, "strigolactones (SLs)", is required to develop the technology for Striga control. This review outlines recent findings on the SL perception mechanism, which have been accumulated in Striga hermonthica by the similarity of the protein components that regulate SL signaling in nonparasitic model plants, including Arabidopsis and rice. HTL/KAI2 homologs were identified as SL receptors in the process of Striga seed germination. Recently, this molecular basis has further promoted the development of various types of SL agonists/antagonists as seed germination stimulants or inhibitors. Such chemical compounds are also useful to elucidate the dynamic behavior of SL receptors and the regulation of SL signaling. [ABSTRACT FROM AUTHOR]

Key message: We find that the DREB subfamily transcription factor, CmERF053, has a novel function to regulate the development of shoot branching and lateral root in addition to affecting abiotic stress.Abstract: Dehydration-responsive element binding proteins (DREBs) are important plant transcription factors that regulate various abiotic stresses. Here, we isolated an APETALA2/ethylene-responsive factor (AP2/ERF) transcription factor from chrysanthemum (Chrysanthemum morifolium ‘Jinba’), CmERF053, the expression of which was rapidly up-regulated by main stem decapitation. Phylogenetic analysis indicated that it belongs to the A-6 group of the DREB subfamily, and the subcellular localization assay confirmed that CmERF053 was a nuclear protein. Overexpression of CmERF053 in Arabidopsis exhibited positive effects of plant lateral organs, which had more shoot branching and lateral roots than did the wild type. We also found that the expression of CmERF053 in axillary buds was induced by exogenous cytokinins. These results suggested that CmERF053 may be involved in cytokinins-related shoot branching pathway. In this study, an altered auxin distribution was observed during root elongation in the seedlings of the overexpression plants. Furthermore, overexpress CmERF053 gene could enhance drought tolerance. Together, these findings indicated that CmERF053 plays crucial roles in regulating shoot branching, lateral root, and drought stress in plant. Moreover, our study provides potential application value for improving plant productivity, ornamental traits, and drought tolerance. [ABSTRACT FROM AUTHOR]

Strigolactones (SLs) are a very special class of plant hormones, which act as endogenous signals to regulate shoot branching in plants, and also serve as rhizosphere signals to regulate interactions of host plants with heterologous organisms such as symbiotic arbuscular mycorrhizal fungi and parasitic weeds. In this short review, we give a brief description of novel discoveries in SL biosynthesis pathway, and mainly summarize the recent advances in SL perception and signal transduction. [ABSTRACT FROM AUTHOR]

Larix kaempferi is an economically and ecologically valuable afforestation and timber species. However, functional genes participating in its growth and development remain largely unknown because of its long growth cycle and highly complex genetic background. In this study, LkAP2L2, an AP2/ERF transcription factor gene, was identified and the characteristics and functions of LkAP2L2 were further explored. The cDNA of LkAP2L2, with a length of 2124 bp, encodes a transcription factor comprising 707 amino acid residues. LkAP2L2 was further introduced into Arabidopsis genome using the Agrobacterium tumefaciens transformation method. The shoot branching phenotype of LkAP2L2-overexpressing Arabidopsis was enhanced. The number of their branches was almost twice as high as that of the vector control plants. In contrast to those on bushier branches, the size and number of rosette leaves were decreased by LkAP2L2 overexpression. In particular, the length of the fifth rosette leaves was shorter by approximately 17% in 35S::LkAP2L2 plants, and the number of rosette leaves was approximately 70% of that of the vector control. In addition, the length of silique was decreased by a half compared with the vector control plants, and no more than 4 seeds per silique were detected in the transgenic plants. The length of siliques and the number of seeds are decreased by LkAP2L2 through its influence on flower development. Therefore, LkAP2L2 of L. kaempferi plays a crucial role in branch, flower, silique and seed development, and this gene may be manipulated to obtain the bushy phenotype of plants. [ABSTRACT FROM AUTHOR]

Cotton ( Gossypium spp.), as the most important fiber and oilseed crop in the world, is extremely important for the industry. However, due to its indeterminate growth habit and complex branching system, massive labor costs are needed for shoot apex removal and branch pruning during cotton production. Therefore, it is very important to explore branch-controlling genes and genetically modify the branch architecture of cotton. Strigolactones (SLs) are a novel class of plant hormone that inhibit the outgrowth of lateral branches. To elucidate the role of SLs in branch development of cotton, we cloned and characterized GhMAX2a and GhMAX2b from tetraploid upland cotton ( Gossypium hirsutum), the orthologs of Arabidopsis MAX2, rice D3, and petunia RMS4. GhMAX2a/2b was ubiquitously expressed in all tested tissues of cotton, with relatively higher expression levels in leaves and lateral buds. Subcellular localization assay showed that the GhMAX2-GFP fusion protein localized to the nucleus. Both GhMAX2a and GhMAX2b can fully rescue the dwarfed and highly branched phenotypes of the Arabidopsis max2-1 mutant, indicating that GhMAX2s have conserved functions with that of AtMAX2. The cotton GhMAX2b interacted with Arabidopsis Skp1-like 1 (ASK1) proteins in vitro which was further confirmed in the Arabidopsis protoplasts using the co-immunoprecipitation assay, indicating that GhMAX2b probably functions through forming an SCF E3 complex with Skp and other proteins in the Arabidopsis. These results suggest that the cotton GhMAX2s encode functional MAX2 that can inhibit the shoot lateral branching. Further functional analysis of GhMAX2s in determining cotton branch architecture and yield is underway. [ABSTRACT FROM AUTHOR]

The morphology of a plant is not predestined during embryonic development and its myriad branching architecture is post-embryonically determined by axillary meristem (AM) activity as the plant adapts to a varying environment. The shoot apical meristem produced during embryonic development repetitively gives rise to a phytomer that comprises a leaf, an AM, and an internode. The final aerial architecture is regulated by shoot branching patterns derived from AM activity. These branching patterns are modulated by two processes: AM formation and axillary bud outgrowth. Several transcription factors (TFs) that regulate these processes have been identified. Various plant hormones, including strigolactones and auxin, have major roles in controlling these TFs. In this review we focus on molecular mechanisms that guide AM initiation and axillary bud growth, using rice as our main species of emphasis. [ABSTRACT FROM AUTHOR]

Shoot branching (tillering) primarily determines plant shoot architecture and has been studied in many plants. Shoot branching is an important trait in non-heading Chinese cabbage ( Brassica rapa ssp. chinensis Makino). The B. rapa ssp. chinensis var. multiceps exhibits unique and multiple shoot branching characteristics. Here, we analyzed the variation in shoot branching between 'Maertou,' with multiple shoot branching, and 'Suzhouqing,' a common variety. The levels of endogenous indole-3-acetic acid (IAA), zeatin riboside and active gibberellins in the shoot meristem tissues of the two cultivars were quantified by enzyme-linked immunosorbent assay during the vegetative growth stage. High levels of IAA maintained axillary bud dormancy and repressed axillary bud outgrowth allowing shoot branching to form in the vegetative stage in 'Suzhouqing.' In contrast, low levels of IAA did not inhibit axillary buds in 'Maertou,' while a high level of cytokinin promoted axillary bud growth and branch shoot development. Exogenous hormone (rac-GR24 and 6-benzylaminopurine) treatment showed that 'Maertou' was relatively sensitive to cytokinin, because the fold changes of cytokinin-responsive genes in 'Maertou' were significantly more frequent than those in 'Suzhouqing'. Cytokinin was the direct regulator for axillary bud growth of 'Maertou'. Compared with 'Suzhouqing', 'Maertou' was sensitive to cytokinin and this weakened the strigolactone-cytokinin branching pathway. [ABSTRACT FROM AUTHOR]

Cremastra appendiculata (D. Don) Makino is a mainly vegetative propagation terrestrial orchid that is a typical representative of the warm-temperate vegetation in China. In this experiment, we investigated the growth and development process of C. appendiculata leaf buds and examined their biochemical components (proteins, auxin, and cytokinin) to gain insight into the 'shoot branching' of C. appendiculata pseudobulb string. The results showed that the metabolic activity of C. appendiculata pseudobulbs became lower with the increase of pseudobulb age. However, biennial and triennial pseudobulbs have higher auxin levels than annual pseudobulbs in the intact plant ( P < 0.05). After decapitation, the auxin rapidly reduces in biennials. The reduction of auxin level promotes cytokinin biosynthesis, which makes the biennial dormant buds start to germinate 18 days after decapitation. These data and phenomena suggested that auxin plays important roles in regulating shoot branching of C. appendiculata, although further studies are needed to consolidate this viewpoint. Our data indirectly support the classical apical dominance theory whereby biennial pseudobulbs are strongly dependent on reduced auxin to initiate leaf bud outgrowth. [ABSTRACT FROM AUTHOR]

SET domain group 8 (SDG8) serves as multifunctional H3 methyltransferase to be involved in various processes in plants. To better understand its functions, an EMS mutagenesis of sdg8- 2 seeds was performed for the enhancers of sdg8- 2, and an allele of CURLY LEAF ( clf100) was identified in the study, which enhanced the phenotype of sdg8- 2, such as early flower, abortion, and more shoot branches. Real-time PCR analysis indicated that the simultaneous disruption of SDG8 and CLF can lead to synergistic or antagonistic effect on transcriptional accumulation of shoot branching regulatory genes. Among the 16 genes examined in the study, the transcriptional accumulation of LATERAL SUPPRESSOR ( LAS) and UDP- GLYCOSYLTRANSFERASE 74E2 ( UGT74E2) displayed most significant enhancement in double mutant. Furthermore, the chromatin immunoprecipitation assay indicated that the excess expressions of LAS and UGT74E2 in double mutant were associated with the state of H3K trimethylation marks at their locus, showing the reduction of H3K27me3 level, as well as an elevated enrichment of H3K36me3 at LAS locus and H3K4me3 at UGT74E2 locus. These results indicated that CLF and SDG8 can play a combinatorial role in regulation of shoot branching via maintaining proper histone markers for appropriate gene expression. [ABSTRACT FROM AUTHOR]

Chrysanthemums are important ornamental plants with abundant phenotypic diversity. Especially in cut-flower breeding, shoot branching is important for the success of new varieties. To assess the genetic regulation of shoot branching and other horticultural important traits, we phenotyped and genotyped two types of chrysanthemum populations: a genotype collection of 86 varieties and a biparental F1-population (MK11/3) of 160 individuals. Using two different statistical approaches, a genome-wide association analysis and a single marker ANOVA, with AFLP marker data and candidate gene markers for shoot branching, we tried to identify markers correlated to the traits of interest. As expected for the outcrossing hexasomic chrysanthemums most of the phenotypic traits showed a continuous variation in both populations. With the candidate gene approach we identified 11 significantly associated marker alleles for all 4 strigolactone pathway genes BRC1, CCD7, CCD8 and MAX2 regulating shoot branching in the genotype collection. In the MK11/3 we detected seven markers for all candidate genes except MAX2 explaining a large proportion of the variation. Using anonymous AFLP markers in the GWA with the 86 genotypes and the single locus analysis with the F1-population we could detect 15 and 17 additional marker-trait associations, respectively. Our analyses indicate a polygenic inheritance of the shoot branching in the chrysanthemum, with a fundamental role of the strigolactone pathway genes BRC1, CCD7, CCD8 and MAX2 and we identified 50 associated markers to all traits under study. These markers could be used in the selection of the parental plants for breeding chrysanthemums to enrich them for positive alleles influencing plant architecture traits. [ABSTRACT FROM AUTHOR]

MicroRNA156 ( miR156) is a regulator of flowering time and biomass production through regulation of members of SQUAMOSA PROMOTER BINDING PROTEIN- LIKE (SPL) gene family. To expand our investigations on the utility of miR156 in alfalfa, we generated transgenic alfalfa expressing a heterologous miR156 from Lotus japonicus ( LjmiR156a). 5′ RACE and qRT-PCR analysis confirmed that the same three SPL genes ( MsSPL6, MsSPL12, and MsSPL13) targeted by MsmiR156d are also targets of LjmiR156a in alfalfa. Ectopic expression of LjmiR156a down-regulated these SPL genes in transgenic alfalfa, coupled with reduced internode length, a more extreme delay in flowering time than occurred with MsmiR156d, enhanced shoot branching, and elevated biomass production. While root length was maintained, nodulation was reduced in some transgenic genotypes. Furthermore, heterologous expression of LjmiR156a enhanced the contents of starch, soluble sugars, and phenolics in all transgenic genotypes in contrast to the impact from MsmiR156d enhancement, even though the effects on lignin, cellulose, pectin, structural sugars, flavonoids, and carotenoids were variable among the new alfalfa genotypes. The variations among the traits/genotypes reflect the change in expression of alfalfa SPL genes targeted by LjmiR156a and show that LjmiR156a could be employed as a tool to improve quality and yield of alfalfa biomass. [ABSTRACT FROM AUTHOR]

Key message: Nitrogen availability and cytokinin could promote shoot branching in rice, whereas auxin and strigolactone inhibited it. The interaction between nitrogen availability and the three hormones is discussed. Abstract: Rice shoot branching is strongly affected by nitrogen availability and the plant hormones auxin, cytokinin, and strigolactone; however, the interaction of them in the regulation of rice shoot branching remains a subject of debate. In the present study, nitrogen and the three hormones were used to regulate rice tiller bud growth in the indica rice variety Yangdao 6. Both nitrogen and CK promoted shoot branching in rice, whereas auxin and SL inhibited it. We used HPLC to determine the amounts of endogenous IAA and CK, and we used quantitative real-time PCR analysis to quantify the expression levels of several genes. Nitrogen enhanced the amount of CK by promoting the expression levels of OsIPTs in nodes. In addition, both nitrogen and CK downregulated the expression of genes related to SL synthesis in root and nodes, implying that the inhibition of SL synthesis by nitrogen may occur at least partially through the CK pathway. SL did not significantly reduce the amount of CK or the expression levels of OsIPT genes, but it did significantly reduce the amount of auxin and the auxin transport capacity in nodes. Auxin itself inhibited CK synthesis and promoted SL synthesis in nodes rather than in roots. Furthermore, we found that CK and SL quickly reduced and increased the expression of FC1 in buds, respectively, implying that FC1 might be a common target for the CK and SL pathways. Nitrogen and auxin delayed expression change patterns of FC1, potentially by changing the downstream signals for CK and SL. [ABSTRACT FROM AUTHOR]

The lateral suppressor ( Ls) genes have a conserved role in axillary meristem initiation in diverse plants. Transgenic chrysanthemum ( Dendranthema × grandiflorum) carrying antisense Ls cDNA was generated using Agrobacterium-mediated transformation. Totally 139 shoots were obtained as transformants, and with 5 transgenic plants selected in the preliminary observation, shoot branching was screened on 3 different planting dates. The number of axillary buds in the transgenic plants was changed over season. Axillary buds were visible in all axils in the April planting, but the number of axillary buds was reduced in the June planting in 3 transformants. The biggest reduction in the number of axillary buds was found in Ls80, whose antisense Ls transcript was the highest. The percentage of axillary buds in Ls80 decreased from 100% to 26% when the planting date was delayed from April 26 to June 15, but increased again to 55.9% on the August 12 planting. Anatomical assay suggest that the loss of axillary buds was as a result of defects in initiating axillary meristem. Transgenic plants carrying the Ls antisense gene displayed several floral morphological differences in comparison with nontransgenic control 'Jinba'. Typical abnormal features in the plants included lobbed petals and a stamen-like structure around the style. We conclude that the Ls gene has a conserved role in axillary meristem initiation in chrysanthemum and might interact with other temperature-dependent genes. [ABSTRACT FROM AUTHOR]

Optimization of plant architecture is important for cultivation and yield of cereal crops in the field. Tillering is an essential factor used to determine the overall architecture of cereal crops. It has long been recognized that the development of branching patterns is controlled by the level and distribution of auxin within a plant. To better understand the relationship between auxin levels and tillering in rice, we examined rice plants with increased or decreased levels of free IAA. To decrease IAA levels, we selected the rice IAA-glucose synthase gene ( OsIAGLU) from the rice genome database based on high sequence homology with IAA-glucose synthase from maize ( ZmIAGLU), which is known to generate IAAglucose conjugate from free IAA. The OsIAGLU gene driven by the Cauliflower Mosaic Virus 35S promoter was transformed into a rice cultivar to generate transgenic rice plants constitutively over-expressing this gene. The number of tillers and panicles significantly increased in the transgenic lines compared to the wild-type plants, while plant height and panicle length decreased. These results indicate that decreased levels of free IAA likely enhance tiller formation in rice. To increase levels of free IAA, we treated rice plants with three different concentrations of exogenous IAA (1 μM, 10 μM and 100 μM) twice a week by spraying. Exogenous IAA treatment at concentrations of 10 μM and 100 μM significantly reduced tiller number in three different rice cultivars. These results indicate that exogenously applied IAA inhibits shoot branching in rice. Overall, auxin tightly controls tiller formation in rice in a negative way. [ABSTRACT FROM AUTHOR]

The lateral buds of non-branching chrysanthemum cultivars are affected by temperature and exogenous plant growth regulator (PGR) treatment. The number of axillary buds, endogenous indole-3-acetic acid (IAA) and t-zeatin riboside (t-ZR) concentrations by planting date and PGR treatments were investigated in three genotypes. Two non-branching genotypes, 'Iwanohakusen' and '01B1-8' and branching type 'Jinba' were planted on May 2 and June 29. 'Jinba' always bore axillary buds and '01B1-8' showed stronger non-branching traits than 'Iwanohakusen'. Only 22.9% viable buds developed in the axils of '01B1-8' whereas 68.7% developed in 'Iwanohakusen' on the May 2 planting date group. When planting was delayed from May 2 to June 29, the number of axillary buds decreased in both non-branching genotypes. Endogenous IAA concentrations remained unchanged and t-ZR concentrations decreased in all the three genotypes when the planting date was delayed. This reduced t-ZR level corresponds to the increased ratio of IAA/t-ZR. The number of viable axillary buds increased from 21.7% to 50.1% upon ethephon treatment and to 30.3% by synthetic cytokinin 6-benzylaminopurine (BAP) treatment in '01B1-8'. Viable axillary buds of '01B1-22' increased from 17.1% to 25.1% and 29.1% respectively. Ethephon and BAP application decreased endogenous IAA contents and increased t-ZR contents. Elevated concentrations of t-ZR rather than IAA probably account for axillary bud formation in non-branching chrysanthemum. Just as the non-branching genotypes, the branching type cultivar 'Jinba' showed similar changes in IAA and t-ZR contents according to planting date and exogenous PGR treatments. These results showed that genotypic difference of branching patterns is not a result of concentration-dependent reaction. [ABSTRACT FROM AUTHOR]

The influence of nodal rooting on branching was studied in three evolutionarily and morphologically diverse species of prostrate clonal herbs: Tradescantia fluminensis (a monocotyledonous extreme 'phalanx' species), Calystegia silvatica (a dicotyledonous extreme 'guerrilla' species) and Trifolium repens (a dicotyledonous intermediate species). In all three, branch development from axillary buds is regulated by a positive signal produced by roots together with inhibitory influences from both pre-existing branches and shoot apical buds (apical dominance). Responses to nodal roots are cumulative and increased root activity leads to more vigorous bud outgrowth. In the absence of nodal roots, a single basal root system is unable to maintain continued extension growth of the shoot. We suggest that as individual nodal roots and stem internodes are both short-lived in these nodally-rooting clonal species, the plants' investment in them is minimal. Thus, in contrast to perennial species lacking nodal roots, individual root systems in prostrate clonal herbs are small and stems have little secondary thickening and development of long-distance transport tissues. Hence the decline in extension growth of the shoot in the absence of nodal roots could be linked to the weak development of long-distance transport tissues in their relatively thin horizontal stems and to resource sharing between primary stems and lateral branches (as suggested by the greater retardation of primary stem growth in the more profusely branched 'phalanx' species ( Trifolium and Tradescantia) than in the weakly branched 'guerrilla' species, Calystegia). These findings are consistent with the view that the long-term persistence of genotypes of nodally-rooting prostrate species is dependent upon them encountering the moist conditions required to facilitate the continual development of new young nodal root systems. [ABSTRACT FROM AUTHOR]

Shoot branching and growth are controlled by phytohormones such as auxin and other components in Arabidopsis. We identified a mutant ( igi1) showing decreased height and bunchy branching patterns. The phenotypes reverted to the wild type in response to RNA interference with the IGI1 gene. Histochemical analysis by GUS assay revealed tissue-specific gene expression in the anther and showed that the expression levels of the IGI1 gene in apical parts, including flowers, were higher than in other parts of the plants. The auxin biosynthesis component gene, CYP79B2, was up-regulated in igi1 mutants and the IGI1 gene was down-regulated by IAA treatment. These results indicated that there is an interplay regulation between IGI1 and phytohormone auxin. Moreover, the expression of the auxin-related shoot branching regulation genes, MAX3 and MAX4, was down-regulated in igi1 mutants. Taken together, these results indicate that the overexpression of the IGI1 influenced MAX pathway in the shoot branching regulation. [ABSTRACT FROM AUTHOR]

Strigolactones have recently been identified as the long sought-after signal required to inhibit shoot branching (Gomez-Roldan et al .; Umehara et al .; reviewed in Dun et al .). Here we briefly describe the evidence for strigolactone inhibition of shoot branching and, more extensively, the broader context of this action. We address the central question of why strigolactone mutants exhibit a varied branching phenotype across a wide range of experimental conditions. Where knowledge is available, we highlight the role of other hormones in dictating these phenotypes and describe those instances where our knowledge of known plant hormones and their interactions falls considerably short of explaining the phenotypes. This review will focus on bud outgrowth in herbaceous species because knowledge on the role of strigolactones in shoot branching to date barely extends beyond this group of plants. [ABSTRACT FROM AUTHOR]

The ratio of auxin and cytokinin plays a crucial role in regulating aerial architecture by promoting or repressing axillary bud outgrowth. We have previously identified an Arabidopsis mutant bud2 that displays altered root and shoot architecture, which results from the loss-of-function of S-adenosylmethionine decarboxylase 4 (SAMDC4). In this study, we demonstrate that BUD2 could be induced by auxin, and the induction is dependent on auxin signaling. The mutation of BUD2 results in hyposensitivity to auxin and hypersensitivity to cytokinin, which is confirmed by callus induction assays. Our study suggests that polyamines may play their roles in regulating the plant architecture through affecting the homeostasis of cytokinins and sensitivities to auxin and cytokinin. [ABSTRACT FROM AUTHOR]

The lateral suppressor-like gene DgLsL was transformed by agroinfection into chrysanthemum in both the sense and antisense directions. Sense transformants branched more profusely than the wild-type nontransformant, while branching in the antisense transformants was significantly suppressed. An analysis of DgLsL transcript abundance in the shoot tips revealed that expression was enhanced in the sense transformants and suppressed in the antisense ones. The shoot tip content of indole-3-acetic acid (IAA) was reduced in the sense transformants but enhanced in the antisense ones. The sense transformants had a lower content and the antisense transformants had a higher content of gibberellic acid (GA). Cytokinin content was not affected by the variation in DgLsL expression. We conclude that DgLsL controls shoot branching through its effect on IAA and GA levels. [ABSTRACT FROM AUTHOR]

Because plants are sessile organisms, the ability to adapt to a wide range of environmental conditions is critical for their survival. As a consequence, plants use hormones to regulate growth, mitigate biotic and abiotic stresses, and to communicate with other organisms. Many plant hormones function pleiotropically in vivo, and often work in tandem with other hormones that are chemically distinct. A newly-defined class of plant hormones, the strigolactones, cooperate with auxins and cytokinins to control shoot branching and the outgrowth of lateral buds. Strigolactones were originally identified as compounds that stimulated the germination of parasitic plant seeds, and were also demonstrated to induce hyphal branching in arbuscular mycorrhizal (AM) fungi. AM fungi form symbioses with higher plant roots and mainly facilitate the absorption of phosphate from the soil. Conforming to the classical definition of a plant hormone, strigolactones are produced in the roots and translocated to the shoots where they inhibit shoot outgrowth and branching. The biosynthesis of this class of compounds is regulated by soil nutrient availability, i.e. the plant will increase its production of strigolactones when the soil phosphate concentration is limited, and decrease production when phosphates are in ample supply. Strigolactones that affect plant shoot branching, AM fungal hyphal branching, and seed germination in parasitic plants facilitate chemical synthesis of similar compounds to control these and other biological processes by exogenous application. [ABSTRACT FROM AUTHOR]