Kang Il-Ho, Steffen Joshua G, Portereiko Michael F, Lloyd Alan, Drews Gary N
Department of Biology, University of Utah, Salt Lake City, Utah 84112-0840, USA.
Plant Cell. 2008 Mar;20(3):635-47. doi: 10.1105/tpc.107.055137. Epub 2008 Mar 11.
Endosperm, a storage tissue in the angiosperm seed, provides nutrients to the embryo during seed development and/or to the developing seedling during germination. A major event in endosperm development is the transition between the syncytial phase, during which the endosperm nuclei undergo many rounds of mitosis without cytokinesis, and the cellularized phase, during which cell walls form around the endosperm nuclei. The molecular processes controlling this phase transition are not understood. In agl62 seeds, the endosperm cellularizes prematurely, indicating that AGL62 is required for suppression of cellularization during the syncytial phase. AGL62 encodes a Type I MADS domain protein that likely functions as a transcription factor. During seed development, AGL62 is expressed exclusively in the endosperm. During wild-type endosperm development, AGL62 expression is strong during the syncytial phase and then declines abruptly just before cellularization. By contrast, in mutant seeds containing defects in some FERTILIZATION-INDEPENDENT SEED (FIS) class Polycomb group genes, the endosperm fails to cellularize and AGL62 expression fails to decline. Together, these data suggest that AGL62 suppresses cellularization during the syncytial phase of endosperm development and that endosperm cellularization is triggered via direct or indirect AGL62 inactivation by the FIS polycomb complex.
胚乳是被子植物种子中的一种贮藏组织，在种子发育过程中为胚提供营养，和/或在种子萌发过程中为发育中的幼苗提供营养。胚乳发育中的一个主要事件是从合胞体阶段到细胞化阶段的转变，在合胞体阶段，胚乳核经历多轮有丝分裂但不进行胞质分裂，而在细胞化阶段，胚乳核周围形成细胞壁。控制这一阶段转变的分子过程尚不清楚。在agl62种子中，胚乳过早细胞化，这表明AGL62是合胞体阶段抑制细胞化所必需的。AGL62编码一种I型MADS结构域蛋白，可能作为转录因子发挥作用。在种子发育过程中，AGL62仅在胚乳中表达。在野生型胚乳发育过程中，AGL62在合胞体阶段表达强烈，然后在细胞化前突然下降。相比之下，在一些非受精种子（FIS）类多梳蛋白组基因存在缺陷的突变种子中，胚乳未能细胞化，AGL62表达也未能下降。这些数据共同表明，AGL62在胚乳发育的合胞体阶段抑制细胞化，并且胚乳细胞化是由FIS多梳复合体直接或间接使AGL62失活触发的。
