真核生物非编码小RNA分子通过介导mRNA降解、抑制蛋白质翻译和染色质修饰负调控靶标基因的表达。小RNA在植物的生长发育，信号转导以及生物和非生物胁迫反应中起重要调控作用。
siRNA机制
中科院微生物所植物基因组国家重点实验室方荣祥院士研究组在对水稻MAIF1(miRNAs regulated and abiotic stress induced F-box gene) 基因的研究中发现：该基因受植物激素脱落酸(abscisic acid，ABA)和干旱、高盐等非生物胁迫因素的诱导启动表达，同时又受小RNA（siR441 和 siR446）的转录后调控。
miR441和miR446过去被注释为microRNA，因为其前体可以形成典型的茎环结构，但是它们又不被认为是真正的miRNA，因为它们与植物miRNA的注释规则不一致。于是，研究人员暂且称之为小干扰RNA——siR441和siR446。
作为MAIF1的负调控子，siR441 和 siR446的表达量受ABA和非生物胁迫抑制，但是令人感到意外的是其前体RNA的积累却显著增加了。深入研究证明：siR441 和 siR446存在一个自我调控的过程，即当siR441 和siR446的前体RNA的表达量升高时会形成一种自我配对现象，该配对影响了其被正确剪切，使得成熟小RNA的量不升反而降低。
这种自我调控的机制的阐明部分回答了一个尚未被普遍研究的科学问题，即作为负调控因子的小RNA自身是如何被调控的。
该项研究结果于近日发表在The Plant Journal杂志上。
生物探索推荐英文原文摘要：
Volume 65, Issue 5, pages 820–828, March 2011
Small RNAs from MITE-derived stem-loop precursors regulate abscisic acid signaling and abiotic stress responses in rice
摘要：
Small silencing RNAs (sRNAs) are non-coding RNA regulators that negatively regulate gene expression by guiding mRNA degradation, translation repression or chromatin modification. Plant sRNAs play crucial roles in various developmental processes, hormone signaling, immune responses and adaptation to a variety of abiotic stresses. miR441 and miR446 were previously annotated as microRNAs (miRNAs) because their precursors can form typical stem-loop structures, but are not considered as real miRNAs because of inconsistency with some ancillary criteria of the recent guidelines for annotation of plant miRNAs. We tentatively rename them small interfering (si)R441 and siR446, respectively, in this study. It has recently been shown that the precursors of siR441 and siR446 might originate from the miniature inverted-repeat transposable element (MITE) Stowaway1. In this report, we show that, in contrast with Dicer-like (DCL)3- and RNA-dependent RNA polymerase (RDR)2-dependent MITE-derived ra-siRNAs, siR441 and siR446 are processed by OsDCL3a but independent of OsRDR2, indicating that siR441 and siR446 are generated from single-stranded stem-loop precursors. We also show that abscisic acid (ABA) and abiotic stresses downregulate the expression of siR441 and siR446 but, surprisingly, increase the accumulation of their precursors in rice plants, implying that processing of siRNA precursors is inhibited. We provide evidence to show that this defective processing is due to increased precursor accumulation per se, possibly by intermolecular self-pairing of the processing intermediate sequences, thus hindering their normal processing. Functional examinations indicate that siR441 and siR446 are positive regulators of rice ABA signaling and tolerance to abiotic stress, possibly by regulating MAIF1 expression.
