Molecular mechanisms of shoot apical meristem formation

双子叶植物的幼苗有两个子叶、下子叶和胚根，由顶端向基部排列。下胚轴根的末端分别有茎和根的顶端分生组织。这些组织中的细胞继续分裂，茎尖分生组织中的部分细胞依次分化为侧枝器官和茎，根分生组织萌发后不断产生根。本课题旨在研究拟南芥胚发生过程中茎尖分生组织形成和侧根分生组织形成的分子机制。我们可以成功地得到下面两个有趣的结果。1、SAM形成；CUC 1, 2 （CUP形子叶1,2）基因在胚胎发生过程中是SAM形成的冗余必需基因，其功能是转录激活因子。CUC1的异位表达引起子叶和叶片的不定芽诱导。在这些过程中，CUC1异位诱导STM （SHOOT MELISTEMLESS）基因表达。CUC1和CUC2基因对愈伤组织的后期不定芽诱导均有较好的效果。2、RAM形成；新的根分生组织在侧根诱导前发育。植物激素生长素在这个过程中很重要。新的转录调节因子SLR（孤根）介导生长素信号诱导中柱鞘细胞侧根分生组织，重新开始细胞分裂。该基因的显性突变体（slr）完全丧失了诱导侧根的能力。我们分离了slr抑制子，并对其中一个slr抑制子进行了遗传分析，该抑制子编码一种推测的染色质重塑因子。

Seedling of dicotyledonous plant has two cotyledons, hypocotyl and embryonic root arranging from the apical to basal. There is a shoot and root apical meristems at the end of hypocotyl root, respectively. Cells in these tissues continue to divide and some of them in the shoot apical meristem are differentiated into lateral organs and stem in turn and root meristem produces root continuously after germination. The purpose of this project is to make clear molecular mechanisms of shoot apical meristem formation during embryogenesis and of lateral root meristem formation using Arabidopsis. We can succeed to get next two interesting results.1, SAM formation ; CUC 1, 2 (CUP SHAPED COTYLEDONS 1, 2) genes, which are redundantly essential for SAM formation during embryogenesis, are functioned as transcription activators. Ectopic expression of CUC1 caused adventitious shoot induction on cotyledons and leaves. In these processes, CUC1 induced STM (SHOOT MELISTEMLESS) gene expression ectopically. Both CUC1 and CUC2 genes an excel late adventitious shoot induction from callus.2, RAM formation ; A new root meristem was developed before induction of a lateral root. Phytohormone auxin is important in this process. The novel transcription regulator SLR (SOLITARY ROOT) mediates auxin signal to induce the lateral root meristem from pericycle cells, which re-start cell division. The dominant mutant of this gene (slr) completely lost the ability to induce the lateral root. Suppressors of slr were isolated and one of them was analyzed genetically, which encodes one of the putative chromatin remodeling factors.