Project description:Plant inflorescence meristems and floral meristems possess specific boundary domains that result in floral organ separation, and in proper numbers of floral organs. HANABA TARANU (HAN) encodes a boundary-expressing GATA type zinc finger transcription factor that regulates shoot apical meristem organization, cell division and flower development in Arabidopsis, but the underlying mechanism remains unclear. Through time-course whole genome oligonucleotide microarray analyses following transient overexpression of HAN, we find that HAN represses hundreds of genes, especially genes involved in hormone responses and floral organ regulation. Transient overexpression of HAN also causes the repression of HAN itself and three other HAN family genes: HANL2 (HAN-LIKE2), GNC (GATA, NITRATE-INDUCIBLE, CARBON-METABOLISM-INVOLVED) and GNL (GNC LIKE), forming a negative regulatory feedback loop. Double- and triple-mutant strains of han with hanl2, gnc and gnl show synergistic effects on sepal fusion, petal number, and silique length, and embryo development, as well as carpelloid stamens. Transcripts of HANL2, GNC and GNL have similar accumulation patterns, specifically in petals, stamens, carpels and inflorescence meristems, which are partially overlapping with the expression pattern of HAN, suggesting that HAN and HAN family genes share redundant functions during flower development. We further show by yeast two hybrid assays that HAN can homodimerize as well as heterodimerize with other HAN family proteins. Chromatin-immunoprecipitation analyses indicate that HAN directly binds to its own promoter and the promoter of GNC in vivo. These findings, together with the fact that constitutive overexpression of HAN has an even stronger phenotype than a loss of function mutation, support the hypothesis that HAN may function as a key repressor that regulates floral development via intricate regulatory networks involving genes in the GATA3 family, hormone actions and floral organ specification. Time course induction experiment. Arabidopsis inflorescences containing flower buds from stages 1-9 were collected for microarray experiment 0h, 4h, 12h and 72h after 10M-BM-5M Dex treatment. RNA samples from mock- and Dex-treated plants at each time point were co-hybridized, and labeling dyes were swapped between replicates to reduce dye-related bias. Four biological replicates were used for the microarray hybridization.

Project description:Jatropha curcas L. is a potential biofuel plant. Application of exogenous cytokinin (6-benzyladenine, BA) on its inflorescence buds can significantly increase the number of female flowers, thereby improving seed yield. To investigate which genes and signal pathways are involved in the response to cytokinin in J. curcas inflorescence buds, we monitored transcriptional activity in inflorescences at 0, 3, 12, 24, and 48 h after BA treatment using a microarray. We detected 5,555 differentially expressed transcripts over the course of the experiment, which could be grouped into 12 distinct temporal expression patterns. We also identified 31 and 131 transcripts in J. curcas whose homologs in model plants function in flowering and phytohormonal signaling pathways, respectively. According to the transcriptional analysis of genes involved in flower development, we hypothesized that BA treatment delays floral organ formation by inhibiting the transcription of the A, B and E classes of floral organ-identity genes, which would allow more time to generate more floral primordia in inflorescence meristems, thereby enhancing inflorescence branching and significantly increasing flower number per inflorescence. BA treatment might also play an important role in maintaining the flowering signals by activating the transcription of GIGANTEA (GI) and inactivating the transcription of CONSTITUTIVE PHOTOMORPHOGENIC 1 (COP1) and TERMINAL FLOWER 1b (TFL1b). In addition, exogenous cytokinin treatment could regulate the expression of genes involved in the metabolism and signaling of other phytohormones, indicating that cytokinin and other phytohormones jointly regulate flower development in J. curcas inflorescence buds. Our study provides a framework to better understand the molecular mechanisms underlying changes in flowering traits in response to cytokinin treatment in J. curcas inflorescence buds. The results provide valuable information related to the mechanisms of cross-talk among multiple phytohormone signaling pathways in woody plants.

Project description:Jatropha curcas L. is a potential biofuel plant. Application of exogenous cytokinin (6-benzyladenine, BA) on its inflorescence buds can significantly increase the number of female flowers, thereby improving seed yield. To investigate which genes and signal pathways are involved in the response to cytokinin in J. curcas inflorescence buds, we monitored transcriptional activity in inflorescences at 0, 3, 12, 24, and 48 h after BA treatment using a microarray. We detected 5,555 differentially expressed transcripts over the course of the experiment, which could be grouped into 12 distinct temporal expression patterns. We also identified 31 and 131 transcripts in J. curcas whose homologs in model plants function in flowering and phytohormonal signaling pathways, respectively. According to the transcriptional analysis of genes involved in flower development, we hypothesized that BA treatment delays floral organ formation by inhibiting the transcription of the A, B and E classes of floral organ-identity genes, which would allow more time to generate more floral primordia in inflorescence meristems, thereby enhancing inflorescence branching and significantly increasing flower number per inflorescence. BA treatment might also play an important role in maintaining the flowering signals by activating the transcription of GIGANTEA (GI) and inactivating the transcription of CONSTITUTIVE PHOTOMORPHOGENIC 1 (COP1) and TERMINAL FLOWER 1b (TFL1b). In addition, exogenous cytokinin treatment could regulate the expression of genes involved in the metabolism and signaling of other phytohormones, indicating that cytokinin and other phytohormones jointly regulate flower development in J. curcas inflorescence buds. Our study provides a framework to better understand the molecular mechanisms underlying changes in flowering traits in response to cytokinin treatment in J. curcas inflorescence buds. The results provide valuable information related to the mechanisms of cross-talk among multiple phytohormone signaling pathways in woody plants. Gene expression of flower buds in response to BA was measured at 0h, 3h, 12h, 24h and 48h after 1mM 6-benzylaminopurine treatment. Three biological replicates were prepared for each time point.

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Transcription repressor HANABA TARANU (HAN) controls flower development via integrating multiple hormone actions, floral organ specification and GATA3 family auto-regulation

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