Identification of ta-siRNAs and Cis-nat-siRNAs in Cassava and Their Roles in Response to Cassava Bacterial Blight

Trans-acting small interfering RNAs （ta-siRNAs） and natural cis-antisense siRNAs （cisnat-siRNAs） are recently discovered small RNAs （sRNAs） involved in post-transcriptional gene silencing, ta-siRNAs are transcribed from genomic loci and require processing by microRNAs （miRNAs）. cis-nat-siRNAs are derived from antisense RNAs produced by the simultaneous tran- scription of overlapping antisense genes. Their roles in many plant processes, including pathogen response, are mostly unknown. In this work, we employed a bioinformatic approach to identify ta-siRNAs and cis-nat-siRNAs in cassava from two sRNA libraries, one constructed from healthy cassava plants and one from plants inoculated with the bacterium Xanthomonas axonopodis pv. manihotis （Xam）. A total of 54 possible ta-siRNA loci were identified in cassava, including a homo- log of TAS3, the best studied plant ta-siRNA. Fifteen of these loci were induced, while 39 were repressed in response to Xam infection. In addition, 15 possible c/s-natural antisense transcript （cis-NAT） loci producing siRNAs were identified from overlapping antisense regions in the genome, and were found to be differentially expressed upon Xam infection. Roles of sRNAs were predicted by sequence complementarity and our results showed that many sRNAs identified in this work might be directed against various transcription factors. This work represents a significant step toward understanding the roles of sRNAs in the immune response of cassava.

内源小RNAs在植物胁迫反应中的作用

世界范围内,农作物的产量都容易受到各种生物和非生物因素的影响,对植物逆境适应性反应机制的深入研究有助于我们采取新的措施,以提高作物的逆境适应性。以前通常认为植物适应逆境胁迫的机制主要涉及相关基因在转录水平的调节,然而,近来发现部分内源小RNAs(siRNAs),如miRNAs、nat-siRNAs和lsiRNAs不仅可以调节植物的生长发育,而且在植物逆境反应中具有重要作用。文章就这些内源小RNAs在氧、矿质元素、干旱、低温、脱落酸、机械、重金属、生物及其他环境因素胁迫中的作用机制做一概述。

内源小RNAs在植物病原体抗性反应中的作用

内源小RNAs是动植物基因表达的重要调节分子,它们可以通过指导mRNA的降解、抑制翻译或染色体修饰等机制,在转录水平或转录后水平或两个水平沉默基因。内源小RNAs在植物生长发育和生物和非生物胁迫适应反应中具有重要作用,其中3种内源性的小RNAs参与了植物基本免疫反应和对病原体的特异性免疫反应。内源小RNAs的发现为植物抗菌和抗病研究开辟了新思路,就这几种内源性的小RNAs的产生和它们在植物抗病原体反应中的作用做一概述。

植物小RNAs的研究进展

小RNAs(长度小于40nt)是nc-RNAs重要的一部分,现在植物中已发现了多种小RNAs,如小干扰RNAs(siRNAs)、微小RNAs(miRNAs)、反式作用的小干扰RNAs、天然反义转录小干扰RNAs、异染色质小干扰RNAs、长小片段小干扰RNAs、天然反义转录的微小RNAs及其一些未命名的小RNAs。成熟的小RNAs聚集相关的蛋白质因子,可以抑制转录,导致转录水平的基因沉默(TGS);或介导目标mRNA的剪切,抑制翻译,导致转录后水平基因沉默(PTGS)。

天然反义转录物(NAT)来源的小分子RNA

天然反义转录物(natural antisense transcript,NAT)通常指自然情况下生物体内生成的内源RNA,它们可以与其他RNA部分或完全互补。NAT在生物中非常普遍,并且可以产生多种具有调节作用的小RNA,如天然反义转录干扰小RNA、天然反义微RNA、长的干扰短RNA、扫描RNA和与Piwi相互作用的RNA等。这些小RNA或许是NAT调节基因表达的重要物质分子之一。本文就NAT来源的小RNA及其功能作一概述。