2012年3月9日，《植物细胞》（The Plant Cell）杂志在线发表了中科院上海植生所植物分子遗传国家重点实验室薛红卫研究组的最新研究成果。这篇题为“The MADS29 Transcription Factor Regulates the Degradation of the Nucellus and the Nucellar Projection during Rice Seed Development ”论文揭示了转录因子MADS29是如何通过影响母体组织降解调控种子发育的。

水稻种子是人类重要的食物来源，其发育涉及一个复杂的调控网络，其中转录因子发挥了关键作用。MADS转录因子家族成员是植物花器官发育的重要调控因子，已有的研究表明几乎所有的水稻MADS基因都在种子中表达，但对MADS家族成员参与水稻种子发育调控的研究结果仍比较少。

在这项研究中，该研究组基于前期的表达谱研究基础，分析得到了一个在水稻生殖发育阶段优先表达的转录因子MADS29。细致分析表明MADS29在花药、胚珠和种子中均表达，且在受精后的母体组织表达量最高。MADS29的反义转基因植株呈现种子皱缩，淀粉粒形态异常，灌浆速率下降等表型。通过解剖学切片、末端转移酶标记实验和全基因组表达谱芯片分析等证明了MADS29通过调控程序化死亡(PCD)过程促进珠心细胞和珠心突起处的降解。进一步的体外凝胶阻滞实验显示MADS29能够通过直接结合程序化死亡相关基因的启动子区域而调控其表达，进而影响胚乳发育。这些结果鉴定了一个参与珠心细胞和珠心突起处降解的调控因子，证实这两处组织的降解是水稻种子正常灌浆的前提，并且提示了生长素(IAA)信号在母体组织降解和胚乳发育中的作用，有助于进一步了解水稻种子发育特别是胚乳发育调控的分子机制。

论文摘要：

The MADS box transcription factors are critical regulators of rice (Oryza sativa) reproductive development. Here, we here report the functional characterization of a rice MADS box family member, MADS29, which is preferentially expressed in the nucellus and the nucellar projection. Suppressed expression of MADS29 resulted in abnormal seed development; the seeds were shrunken, displayed a low grain-filling rate and suppressed starch biosynthesis, and contained abnormal starch granules. Detailed analysis indicated that the abnormal seed development is due to defective programmed cell death (PCD) of the nucellus and nucellar projection, which was confirmed by a TUNEL assay and transcriptome analysis. Further studies showed that expression of MADS29 is induced by auxin and MADS29 protein binds directly to the putative promoter regions of genes that encode a Cys protease and nucleotide binding site–Leu-rich repeat proteins, thereby stimulating the PCD. This study identifies MADS29 as a key regulator of early rice seed development by regulating the PCD of maternal tissues. It provides informative clues to elucidate the regulatory mechanism of maternal tissue degradation after fertilization and to facilitate the studies of endosperm development and seed filling.

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