茶树中亚硒酸盐、硒酸盐代谢与转运机制的转录组学研究

Better knowledge of selenium metabolism and transportation in plants is crucial for solving problem of nutritional selenium deficiency and environmental selenium pollution. Selenate and selenite is the most important forms of available selenium in soil，and the mechanisms of their metabolism and transportation are not quite understood in woody plant. Therefore, we proposed the ideas to better understand the process of selenium metabolism in selenium-enriched tea at both physiological and molecular level. The project will firstly explore the effects of several factors influencing selenium absorption and transportation in NaSeO3 or NaSeO4 medium using single factor experiments and orthogonal experiments, which may help to understand physiological pattern of selenium metabolism and transportation. Then, sulfate, NaSeO4 or NaSeO3 is added to the corresponding container with optimized quid culture to form 4 treatments: (1) control 1, XXMY solution without sulfate, XXMY-S; (2) control 2, XXMY solution with sulfate; (3) NaSeO3, XXMY-S solution with NaSeO3; (3) NaSeO4, XXMY-S solution with NaSeO4. Both shoot and root materials from each group are collected for RNA sequencing and selenium concentration analysis. On the base of comparative transcriptome profiling, genes differentially expressed in sample from NaSeO3 or NaSeO4 treatment will be identified in high throughput manner, and some of highly differential expression genes will be chosen to characterize their expression patterns and function. Combining selenium change curve and selenium-related gene expression patterns from different treatment time, we can comprehensively understand the physiological and genetic difference that tea plant response to NaSeO3 and NaSeO4. This project will give insights into mechanisms of selenite and selenate responses in woody plants. It will also provide new targets and strategies for genetic engineering in tea for biofortification purpose.

认识植物的硒代谢与转运对解决人体硒营养缺乏及环境硒污染等问题有重要意义。硒酸盐和亚硒酸盐是土壤中被植物吸收的主要硒形态,目前对于两者在木本植物中的代谢、转运分子机制知之甚少。本项目拟以富硒茶为材料从生理和转录水平探究茶对NaSeO3、NaSeO4的代谢与转运过程。首先，利用单因素法及正交实验探索不同因素对茶苗吸收、积累NaSeO3或NaSeO4的影响。其次，在最佳实验条件下用NaSeO3、NaSeO4培养茶苗，采集不同时间段的地上部分和根样本，测量各样本的硒含量变化，同时进行转录组测序。通过不同转录组间比较可高效筛选与硒代谢、转运相关的差异表达基因并鉴定新基因的功能。结合硒吸收与积累的变化曲线和不同处理时间的基因表达谱，比较茶响应亚硒酸盐、硒酸盐的生理遗传机制差异。本项目对揭示木本植物的亚硒酸盐、硒酸盐的代谢与转运机制有重要意义，也为茶的富硒强化提供优异基因和新策略。

硒酸盐和亚硒酸盐是土壤中易被植物吸收的主要硒形态，目前对于两者在木本植物中的转运与代谢分子机制仍知之甚少。本项目以水培的黔茶601茶苗为材料，利用单因素法及正交实验探索了不同因素对茶苗硒积累的影响，并从生理生化层面探究茶对亚硒酸钠和硒酸钠的转运与代谢过程及其施硒效应。在此基础上，还利用RNASeq进行比较转录组分析以鉴定茶树叶部和根部在不同硒源及不同时间的硒特异响应相关基因并研究其表达模式。结果表明，硒酸钠和亚硒酸钠被根部吸收后，二者在体内可以相互转化，并进入共有硒化合物代谢通路，形成的硒代氨基酸主要形态为硒代半胱氨酸和硒代蛋氨酸，以及少量的硒甲基半胱氨酸。硒化合物代谢、GSH及NADPH形成相关的基因在硒处理中高表达。此外，KEGG分析显示，亚硒酸盐特异性响应上调基因主要富集在“过氧化物酶体”，“内质网蛋白加工”，“囊泡运输的SNARE互作”，“泛素介导的蛋白质降解”，“MAPK信号途径”，而硒酸盐特异性响应基因主要在“剪接体”中有富集。上述结果说明亚硒酸盐与亚硒酸盐有不同的硒响应分子网络并产生不同施硒反应。这进一步佐证了亚硒酸盐在体内转化为硒酸盐需要氧化酶催化，该过程需要消耗氧气形成过氧化氢。总而言之，茶树富硒栽培以硒酸盐作为硒源更优，有利于硒的迁移以及减少根部缺氧及硒胁迫风险。本研究有助于了解亚硒酸盐和硒酸盐的代谢与转运机制及其施硒效应，为富硒茶的基础研究和富硒栽培提有益参考。