解析糖信号调控SnRK1/mTOR通路与毛竹笋竹秆形快速生长的关系

Phyllostachys heterocycla plays a very important role in amelioration of the ecological environment, and in economic prosperity of the mountainous area, and income increase of the farmers. With the support of National Natural Science Foundation of China, we investigated the structure and photosynthetic characteristics of the chloroplasts in the culm and the ultrastructure of the plastids in the rhizome of P. heterocycla, and observed abundant starch grains in the chloroplasts of the culm and in the plastids of the rhizome. Further, we observed at dusk a notable increase in the activity of β-amylase and the debranching enzyme and the formation of autophagosomes in the culm. In this project, in order to further reveal the relationship between the rapid growth of culm and starch grain decomposition and autophagy in the culm and rhizome of P. heterocycla, we will compare the difference of sugar signal substances in culm and rhizome under different growth period of P. heterocycla, and studied the activity of SnRK1/mTOR regulated by sugar signals through in vivo and in vitro experiments. Measurements of endogenous hormones, amylase activity, and the autophagosome-forming capacity verified the contribution of starch grain decomposition in the culm and rhizome to the rapid growth of culm via regulation of the activity of SnRK1/mTOR by sugar signals. These results provide new insights into the mechanism of rapid growth of P. heterocycla and the breeding of fast-growing trees.

毛竹在改善生态环境、繁荣山区经济和增加农民收入等方面起着十分重要的作用。在国家自然科学基金资助下，我们对毛竹茎秆叶绿体结构、光合特性以及竹鞭质体超微结构等方面开展了大量的研究工作，毛竹笋竹茎秆和竹鞭质体中具有丰富的淀粉粒；黄昏后笋竹茎秆内β-淀粉酶和脱支酶活性显著升高，并且有自噬体的形成。为了进一步研究笋竹茎秆和竹鞭质体内淀粉粒分解和自噬与笋竹秆形快速生长的关系，本项目从糖信号调控SnRK1/mTOR通路入手，寻找毛竹笋和成竹与笋竹秆形快速生长过程体内糖信号物质的差异，分别通过体内和体外试验研究糖信号物质对SnRK1/mTOR活性的调控关系；同时研究笋竹茎秆和竹鞭质体内源激素、淀粉分解酶和自噬体形成能力等指标，明确糖信号调控SnRK1/mTOR活性促进笋竹茎秆和竹鞭内淀粉粒分解对笋竹秆形快速生长的贡献。研究成果为进一步明确毛竹速生生长机制以及指导速生树木育种具有重要的意义。

为了探讨毛竹茎秆快速生长过程碳水化合物的变化，本研究采用试剂盒测定了不同时间和部位中可溶性糖和纤维素含量，以及淀粉分解酶活性；采用透射电镜监测了自噬活性，并用实时荧光定量PCR技术测定了BoTPS1和BoSnRK1、PeATG1 和PeATG4、PeAMY和PeBAM基因相对表达，以及光合作用相关基因相对表达量。结果表明：毛竹茎秆快速生长期白天生长慢，夜间生长快；茎秆发育和成熟是是从下往上顺次推进的，基部发育成熟，纤维素沉积较多，中下部生长快速的节间，可溶性糖含量相对较高，上部生长缓慢，淀粉利用较少；竹篼在碳水化合物的运输中起着暂贮和周转作用；毛竹茎秆快速生长与PeBAM基因的表达密切相关，BAM在毛竹茎秆淀粉降解中可能起主要作用。海藻糖含量和BoTPS1基因、BoSnRK1基因的表达量具有一定的偶联关系，T6P/SnRK1 信号在毛竹笋芽快速生长期可能起到重要的调控作用。毛竹茎秆不同时间段的生长发育存在显著差异，夜间有自噬体形成，PeATG1和PeATG4基因表达量较高，茎秆生长迅速。自噬相关基因调控自噬过程的发生，调节毛竹茎秆不同时间段和不同节间的生长发育。快速生长阶段毛竹茎秆存在高于叶片的C4光合特征，光合酶活性和相应酶基因表达水平具有明显一致性。该成果为进一步揭示毛竹笋竹秆形快速生长过程淀粉粒分解机制，以及阐明毛竹笋竹秆形快速生长过程SnRK1/ mTOR促进淀粉粒分解的具体途径提供理论依据。