PNAS:中科院植生所巫永睿研究组等发表玉米品质和产量调控研究

摘要 : 2016年9月12日，国际著名学术期刊《美国国家科学院院刊》杂志在线发表了中国科学院上海生命科学研究院植物生理生态研究所巫永睿研究组与美国罗格斯大学Joachim Messing教授研究组合作题为“Maize endosperm-specific transcription factors O2 and PBF network the regulation of protein and starch synthesis”的研究论文。

2016年9月12日，国际著名学术期刊《美国国家科学院院刊》杂志在线发表了中国科学院上海生命科学研究院植物生理生态研究所巫永睿研究组与美国罗格斯大学Joachim Messing教授研究组合作题为“Maize endosperm-specific transcription factors O2 and PBF network the regulation of protein and starch synthesis”的研究论文。研究发现玉米胚乳特异转录因子O2和PBF同时调控储存蛋白和淀粉合成基因表达，为培育高产优质玉米提供了新思路。助理研究员张志勇、杨俊和博士研究生郑喜喜为论文共同第一作者，巫永睿研究员和Joachim Messing教授为论文共同作者。

在作物育种中，营养品质和产量同等重要，然而这两个关键农艺性状常常相互对立。当产量提高时，品质容易下降;当品质提高时，产量受到影响。因此，作物遗传学家和育种工作者始终有着浓厚兴趣希望通过分子和遗传手段使这两个看似矛盾的性状统一起来，产生品质好却不低产的品种。O2和PBF是玉米胚乳特异转录因子，一直以来，不同实验室关于它们的研究主要集中在调控储存蛋白表达方面。玉米主要储存蛋白是醇溶蛋白，占总蛋白的60-70%。由于醇溶蛋白缺乏必需氨基酸赖氨酸和色氨酸，玉米籽粒的蛋白品质很差。o2突变体中醇溶蛋白下降60%，其它富含赖氨酸和色氨酸的蛋白上升，最终使玉米蛋白品质接近牛奶的品质。然而，以o2为基础材料育成的优质蛋白玉米却在推广上遭遇困难，主要原因是o2影响了产量。

我们通过一系列遗传和生化实验发现o2粒重下降的原因是淀粉合成受到影响。在双突变PbfRNAi; o2中，粒重和淀粉合成下降更为显著。通过rna-seq分析，我们发现在单突变和双突变中主要是糖和蛋白代谢途径的基因表达受到显著影响。我们又通过转录激活，EMSA和免疫共沉淀等实验证明了淀粉合成复合体中两个关键基因PPDKs和淀粉合成酶III(SSIII)直接受到O2和PBF调控，SSIIa和SBE1间接受到O2和PBF调控。我们推论这些基因下调的合力导致了淀粉合成的下降，进而影响粒重。该工作证明了O2和PBF同时调控玉米蛋白品质和粒重，提出将来培育优质蛋白玉米可用RNAi直接沉默醇溶蛋白基因，从而避免用o2突变体影响淀粉合成和粒重。


玉米胚乳特异转录因子O2和PBF同时影响蛋白品质和粒重模式图

原文链接：

Maize endosperm-specific transcription factors O2 and PBF network the regulation of protein and starch synthesis

原文摘要：

The maize endosperm-specific transcription factors opaque2 (O2) and prolamine-box binding factor (PBF) regulate storage protein zein genes. We show that they also control starch synthesis. The starch content in the PbfRNAi and o2 mutants was reduced by ∼5% and 11%, respectively, compared with normal genotypes. In the double-mutant PbfRNAi;o2, starch was decreased by 25%. Transcriptome analysis reveals that >1,000 genes were affected in each of the two mutants and in the double mutant; these genes were mainly enriched in sugar and protein metabolism. Pyruvate orthophosphate dikinase 1 and 2 (PPDKs) and starch synthase III (SSIII) are critical components in the starch biosynthetic enzyme complex. The expression ofPPDK1, PPDK2, and SSIII and their protein levels are further reduced in the double mutants as compared with the single mutants. When the promoters of these genes were analyzed, we found a prolamine box and an O2 box that can be additively transactivated by PBF and O2. Starch synthase IIa (SSIIa, encoding another starch synthase for amylopectin) and starch branching enzyme 1 (SBEI, encoding one of the two main starch branching enzymes) are not directly regulated by PBF and O2, but their protein levels are significantly decreased in the o2 mutant and are further decreased in the double mutant, indicating that o2and PbfRNAi may affect the levels of some other transcription factor(s) or mRNA regulatory factor(s) that in turn would affect the transcript and protein levels of SSIIa and SBEI. These findings show that three important traits—nutritional quality, calories, and yield—are linked through the same transcription factors.

doi: 10.1073/PNAS.1613721113

作者：巫永睿

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