硫元素是植物生长发育必不可少的大量元素之一。植物主要通过根从土壤中以硫酸根的形式获取硫元素，并将其转运到植物的不同组织，然后被组织细胞同化利用，参与植物新陈代谢。植物所吸收获得的硫酸根经过硫同化途径被还原为低价硫，然后参与含硫化合物（如半胱氨酸，甲硫氨酸等）的形成，而多余的硫酸根则被运输到其他组织和（或）在细胞的叶泡内储存。
中国科学院西双版纳植物园植物基因功能研究组余迪求研究员领衔的研究小组在microRNA调控拟南芥发育调节研究方面取得新进展，相关成果文章公布在The Plant Journal上。
研究组系统解释了microRNA395如何参与调控硫酸根在拟南芥体内的吸收、转运和同化的生物学过程及其分子机制。
在成熟叶衰老过程中，硫元素一般被认为是不能向幼叶转移的。但是该研究发现，在硫充足的情况下，拟南芥的硫转蛋白SULTR2;1可以将游离态形的硫酸根从老叶转运到正在发育的幼叶。当植物处于硫缺乏条件时，植物的幼叶往往首先表现出缺硫症状（如黄化），这似乎说明硫酸根是不可以转移的。但进一步的研究表明，在缺硫情况下，植物体内MicroRNA395的表达水平被显著地诱导提高。受到诱导的microRNA395迅速而有效地抑制了其靶基因SULTR2;1的表达，从而限制了硫酸根从老叶向新叶的转运。
microRNA395不仅参与硫酸根的转运，而且还在硫酸根的同化途径中起作用。micorRNA395所调控的另外一组靶基因是APS酶，它们在硫同化途径中负责活化硫酸根。在缺硫条件下microRNA395通过抑制APS1和APS4，部分限制了硫酸根进入同化途径。通过高表达microRNA395基因，研究发现转基因植物过量积累了硫酸根，这说明microRNA395参与了硫酸根的积累。
通过生物信息学预测发现，microRNA395在单子叶和双子叶植物中非常保守，并且其所调控的靶基因也是非常保守的。这表明microRNA395参与硫代谢调控的分子机制也适用于其他植物物种。
该研究详尽的阐述了microRNA395如何调控硫酸根在拟南芥叶片中的积累和转运，解释了植物应对缺硫情况的机制，为现代农业耕作提供了一定的理论依据。
生物谷推荐原文出处：
The Plant Journal doi: 10.1111/j.1365-313X.2010.04216.x
MicroRNA395 mediates regulation of sulfate accumulation and allocation in Arabidopsis thaliana
Gang Liang a,b , Fengxi Yang a and Di-Qiu Yu a,*
a Key Laboratory of Tropical Forest Ecology, Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Kunming, Yunnan 650223, PR China
b Graduate University of Chinese Academy of Sciences, Beijing 100049, PR China
Sulfur is a macronutrient necessary for plant growth and development. Sulfate, a major source of sulfur, is taken up by plant roots and transported into different tissues for assimilation. During sulfate limitation, expression of miR395 is significantly up-regulated. miR395 targets two families of genes, ATP Sulfurylases (APS) and Sulfate Transporter2;1 (SULTR2;1, also called AST68), both of which are involved in the sulfate metabolism pathway. Their transcripts are suppressed strongly in miR395-overexpressing transgenic Arabidopsis, which over-accumulates sulfate in the shoot, but not in the root. APS1 knock-down mutants accumulate two-fold more sulfate compared with the wild-type. By constructing APS4-RNAi transgenic plants, we found that silencing the APS4 gene also results in over-accumulation of sulfate. Even though miR395-overexpressing transgenic plants over-accumulate sulfate in the shoot, they display sulfur deficiency symptoms. Additionally, the distribution of sulfate from old to younger leaves is impaired in miR395-overexpressing plants, which is similar to a SULTR2;1 loss-of-function mutant. The aps1-1sultr2;1APS4RNAi triple repressed mutants phenocopied miR395-overexpressing plants. Our research revealed that miR395 is involved in the regulation of sulfate accumulation and allocation by targeting APSs and SULTR2;1, respectively.
