Cloning And Functional Analysis Of Rice Pleiotropic Gene, Ghd7

To survival, plants adjust the process of growth and development to adapt complex environmental signals. In rice, this process often leads to great change of important agronomic traits, which affect final yield. So the issue about the interaction between rice plant and environmental signal has the theory and application significance. In this project, we show that the quantitative trait locus (QTL) Ghd7has major effects on an array of traits in rice, including number of grains per panicle, plant height and heading date. And we reveal that Ghd7functions to integrate the dynamic environmental inputs (such as light quality, day length, temperature, stress) with phase transition, architecture regulation, and stress response to maximize the reproductive success of the rice plant. Our results are performed as follow:1. Cloning of pleiotropic gene Ghd7We obtained the complete transcribed sequence of Ghd7by RACE and found that Ghd7is a new CCT domain gene, which has no significant homology in Arabidopsis. Subcellular localization result confirmed that GHD7is a nuclear protein and represses the transcriptional activity. Using quantitative RT-PCR analysis, we performed that the expression of Ghd7was mainly detected in the emerged leaf blade and displayed a gradient with much higher transcript accumulation in the leaf tip than the leaf base. Moreover, Ghd7was affected by photoperiodic and diurnal rhythm. The Ghd7transcript was much more abundant during the light period than in dark period, especially under long day conditions. And the expression peak performed at dawn under long day conditions. Ghd7suppressed the expression of flowering time genes under long day conditions and delay heading. Ghd7-Ehdl-Hd3a represents a distinct pathway that does not exist in Arabidopsis. We also identified four Ghd7alleles from five varieties by comparative sequencing analysis. Among them, the alleles from HR5and TQ are strong function alleles, ZH11has the weak function allele and the alleles from MDJ8and HJ19has a premature termination and consider as the nonfunctional allele. Meanwhile, we found alleles of Ghd7also associated with the polymorphism of AT-repeat at3’UTR region. We concluded that Ghd7played crucial roles for increasing productivity and adaptability of rice globally.2. The role of Ghd7in riceThe degree of phenotypic effect of Ghd7on heading date and yield traits was quantitatively related to the transcript level, and was also influenced by both environmental conditions and genetic backgrounds. Ghd7regulated plasticity of tiller branching by mediating the PHYB-OsTB1pathway as adaption to shade signal and the protein level of Ghd7was decrease in phyB mutant. Meanwhile, the expression of Ghd7was regulated by various environmental cues and this gene was also involved in regulation of drought stress response. The results suggested that Ghd7serves as a link between the dynamic environmental inputs with phase transition, architecture regulation and stress response to maximize the reproductive success of the rice plant.3. The mechanism study of Ghd7To detect the downstream network of Ghd7, we used OX-Ghd7ZH11, Ami-Ghd7, phyB mutant and wild type plants to perform the RNA-seq analysis in a diurnal approach (dawn, mid-day, dusk and mid-night). To understand the protein interaction of Ghd7, we fusion the GHD7to3xFlag tag and overexpressed in HJ19. Using this transgenetic plants, we identified that Ghd7formed as a450-kDa protein complex in vivo by gel filtration. Meanwhile, Ghd7can interact with HAP genes in yeast, which also have the ability to interact with OsTOC1. Finally, both HAP genes and clock genes were regulated by PHYB in transcript level. The results indicated that the selective of interaction between HAPs, Ghd7and OsTOCl form a robustness system to mediate the crosstalk between the photoperiod and circadian clock. And PHYB modulate this robustness system in transcript and post-translational levels.4. Ghd7affect hormone pathway1) Overexpressed of Ghd7increase the endogenous ABA content, have more sensitive to exogenous ABA and inhibit seed germination.2) Ghd7controlled the OsPIN genes in SAM and repress the endogenous IAA content.3) Ghd7repressed GA2ox genes expression and its function about the plant height and heading date dependent on endogenous GA contents. The results suggested that Ghd7involve in multiple hormone pathways.