GH3 proteins control auxin homeostasis by inactivating excess auxin as conjugates of amino acids and sugars and thereby controlling cellular bioactive auxin. Since auxin regulates many aspects of plant growth and development, regulated expression of these genes offers a mechanism to control various developmental processes. OsMGH3/OsGH3-8 is expressed abundantly in rice florets and is regulated by two related and redundant transcription factors, OsMADS1 and OsMADS6, but its contribution to flower development is not known. We functionally characterize OsMGH3 by overexpression and knock-down analysis and show a partial overlap in these phenotypes with that of mutants in OsMADS1 and OsMADS6. The overexpression of OsMGH3 during the vegetative phase affects the overall plant architecture, whereas its inflorescence-specific overexpression creates short panicles with reduced branching, resembling in part the effects of OsMADS1 overexpression. In contrast, the down-regulation of endogenous OsMGH3 caused phenotypes consistent with auxin overproduction or activated signaling, such as ectopic rooting from aerial nodes. Florets in OsMGH3 knock-down plants were affected in carpel development and pollen viability, both of which reduced fertility. Some of these floret phenotypes are similar to osmads6 mutants. Taken together, we provide evidence for the functional significance of auxin homeostasis and its transcriptional regulation during rice panicle branching and floret organ development.
GH3 蛋白通过将多余的生长素连接上氨基酸或者糖使生长素失活，从而调节胞内活性生长素的水平。生长素参与调节植物生长发育的多个方面，因此对GH3 基因表达的调节为调控不同的发育进程提供了一种机制。 OsMGH3/OsGH3-8 在水稻小花中高丰度表达，并且受到两个相关的冗余转录因子 OsMADS1 和 OsMADS6 的调控，但是OsMGH3 对花发育的影响目前还不明了。我们通过过量表达和抑制表达对OsMGH3 进行功能分析，发现这些转基因株系的表型与OsMADS1 和OsMADS6 相应突变体的表型部分重叠。在营养期过量表达OsMGH3 影响整个植株的株型，而在花中特异过量表达导致穗变短，支梗数目减少，这与过量表达OsMADS1 的效果是部分类似的。相反，下调OsMGH3 的表达导致植株出现生长素过量产生或信号激活的表型，如根在地上节异位发生。OsMGH3 表达抑制的植株，其心皮的发育和花粉的活性受到影响，导致育性降低。部分花的表型与osmads6 突变体类似。综上所述，结果表明生长素的体内平衡有着重要的作用，在水稻穗支梗和花器官发育过程中受到转录调控。