Dessection of developmental program in rice

在水稻茎尖分生组织（shoot apical merisystem， SAM）的形成过程中至少有4个位点（SHL1 ~ SHL4）参与。为了研究SHL基因如何与SAM的维持相关，我们新发现了SHL2的三个弱等位基因SHL2 -6 ~ SHL2 -8和SHL1的一个弱等位基因SHL1 -3。结果表明，SHL1和SHL2基因在SAM的维持中是不可或缺的。此外，它们还调节叶片原基的发育模式。弱的shl等位基因发育出异常的幼苗，在不规则的叶分结构中产生小的线状叶片。弱shl等位基因的幼苗表型与sho突变体相似。shl2-6 sho2的双突变表明sho2在sho2的上游起作用。为了剖析穗和花的发育机制，我们分析了表现出穗和花组织异常的apo1突变体。apo1产生顶生花是由于轴和枝的分生组织同一性的早熟转化。apo1花的小裂片增加，雄蕊减少。大量雌蕊不确定地产生。这些表型表明APO1基因调控生殖期分生组织身份的时间转化。为了阐明根形成的程序，我们鉴定了冠根（不定根）形成缺陷的突变体。有的突变体在根原基伸长上有缺陷，有的突变体不能形成根原基。因此，在根的形成过程中存在许多基因的复杂级联。

We have already revealed that at least four loci (SHL1〜SHL4) are involved in the initiation of shoot apical meristem (SAM) in rice. To address how SHL genes are associated with the maintenance of SAM, we have newly identified three weak alleles, shl2-6〜shl2-8, of SHL2 and one weak allele, shl1-3, of SHL1. It is revealed that SHL1 and SHL2 genes are indispensable for the maintenance of SAM. In addition, they also regulate the developmental pattern of leaf primordia. Weak shl alleles developed abnormal seedlings producing small thread-like leaves in irregular phyllotaxy. The seedling phenotype of weak shl alleles is similar to that of sho mutants. Double mutant of shl2-6 sho2 suggests that SHO2 function upstream of SHO2.For dissecting developmental mechanism of panicle and flower, we have analyzed apo1 mutants showing abnormal organization of panicle and flowers. The apo1 produced terminal flowers due to the precocious transformation of meristem identity in rachis and branches. In apo1 flowers, lodicules were increased but stamens were decreased. A large number of pistils were produced indeterminately. These phenotypes suggest that APO1 gene regulates temporal y the transformation of meristem identity in reproductive phase.To elucidate the program for root formation, we identified mutants defective in crown root (adventitious root) formation. Some mutants have defect in the elongation of root primordia, and the other failed to form root primordia. Thus, there exists a complex cascade of many genes in root formation.