Candela Héctor, Johnston Robyn, Gerhold Abigail, Foster Toshi, Hake Sarah
Plant Gene Expression Center, US Department of Agriculture-Agricultural Research Service, Albany, California 94710, USA.
Plant Cell. 2008 Aug;20(8):2073-87. doi: 10.1105/tpc.108.059709. Epub 2008 Aug 29.
Leaf primordia initiate from the shoot apical meristem with inherent polarity; the adaxial side faces the meristem, while the abaxial side faces away from the meristem. Adaxial/abaxial polarity is thought to be necessary for laminar growth of leaves, as mutants lacking either adaxial or abaxial cell types often develop radially symmetric lateral organs. The milkweed pod1 (mwp1) mutant of maize (Zea mays) has adaxialized sectors in the sheath, the proximal part of the leaf. Ectopic leaf flaps develop where adaxial and abaxial cell types juxtapose. Ectopic expression of the HD-ZIPIII gene rolled leaf1 (rld1) correlates with the adaxialized regions. Cloning of mwp1 showed that it encodes a KANADI transcription factor. Double mutants of mwp1-R with a microRNA-resistant allele of rld1, Rld1-N1990, show a synergistic phenotype with polarity defects in sheath and blade and a failure to differentiate vascular and photosynthetic cell types in the adaxialized sectors. The sectored phenotype and timing of the defect suggest that mwp1 is required late in leaf development to maintain abaxial cell fate. The phenotype of mwp1; Rld1 double mutants shows that both genes are also required early in leaf development to delineate leaf margins as well as to initiate vascular and photosynthetic tissues.
叶原基从具有内在极性的茎尖分生组织起始；近轴面朝向分生组织，而远轴面背向分生组织。近轴/远轴极性被认为是叶片片状生长所必需的，因为缺乏近轴或远轴细胞类型的突变体通常发育出径向对称的侧生器官。玉米（Zea mays）的马利筋荚1（mwp1）突变体在叶鞘（叶片的近端部分）中有近轴化区域。在近轴和远轴细胞类型并列的地方会形成异位叶瓣。HD-ZIPIII基因卷叶1（rld1）的异位表达与近轴化区域相关。mwp1的克隆表明它编码一个KANADI转录因子。mwp1-R与rld1的一个抗微RNA等位基因Rld1-N1990的双突变体表现出一种协同表型，在叶鞘和叶片中存在极性缺陷，并且在近轴化区域未能分化出维管细胞和光合细胞类型。扇形表型和缺陷出现的时间表明，mwp1在叶片发育后期是维持远轴细胞命运所必需的。mwp1; Rld1双突变体的表型表明，这两个基因在叶片发育早期对于界定叶缘以及启动维管组织和光合组织也是必需的。
