RNA是传递生命遗传信息的重要介质。依据RNA是否编码蛋白质, 可分为编码RNA和非编码RNA。作为非编码RNA的核心种类之一, 小RNA在各种生命活动中均发挥重要调控作用, 其产生及功能发挥依赖于不同的DCL、RDR和AGO蛋白。目前, 植物中功能和调控方式较为明确的是以21 nt为主的miRNA和24 nt siRNA, 其它长度和类型的小RNA由于积累水平通常较低, 尚知之甚少。近日, 南方科技大学郭红卫团队发现, 拟南芥(Arabidopsis thaliana)在缺氮等逆境胁迫下可产生大量依赖于DCL2和RDR6的22 nt siRNA。22 nt siRNA与AGO1结合形成效应复合物, 抑制硝酸还原酶基因(NIA1和NIA2)等mRNA的翻译效率, 从而减少植物在营养缺失条件下的能量消耗。这意味着, 当植物遇到不利环境时, 虽然无法通过移动来逃避逆境, 但可通过诱导产生小RNA, 协调和平衡正常的生长发育与胁迫响应。

RNAs can be classified into protein-coding RNAs and non-coding RNAs (ncRNAs). Small non-coding RNAs (sRNAs) are generated by Dicer-LIKEs (DCLs) and RNA Dependent RNA Polymerases (RDRs). They are associated with different ARGONAUTE (AGO) effector complexes and play important regulatory roles in diverse biological processes. 21 nt microRNAs (miRNAs) and 24 nt small interfering RNAs (siRNAs) are the most abundant classes of sRNAs in plants. The mechanisms of their biogenesis and functions are well studied. However, the functions of other less abundant sRNAs remain largely unknown. A recent study from Prof. Hongwei Guo's group at Southern University of Science and Technology showed that a class of 22 nt siRNAs is produced by RDR6 and DCL2 when plants are under certain stress conditions, especially upon nitrogen deficiency. These 22 nt siRNAs are loaded into AGO1 and mediate translational repression of target mRNAs including nitrate reductase structural genes NIA1/2, thereby minimizing energy consumption. This work elegantly shows that plants deploy 22 nt siRNAs to achieve a deliberate balance between growth and defense in response to environmental stress.