Nuclear gene silencing directs reception of long-distance mRNA silencing in Arabidopsis
Nuclear gene silencing directs reception of long-distance mRNA silencing in Arabidopsis
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DOI：
10.1073/pnas.0706701104
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发表时间：
2007-09-11
影响因子：
11.1
通讯作者：
Carroll, B. J.
中科院分区：
文献类型：
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作者：
Brosnan, C. A.;Mitter, N.;Carroll, B. J.
在植物中，mRNA的沉默可以从一个细胞传递到另一个细胞，也可以通过从根到芽的更长距离传递。为了研究这一长距离机制，将WT和突变体的新芽嫁接到沉默的根上，以获得一种mRNA。我们发现，参与染色质沉默途径的三个基因，编码RNA聚合酶IVa的NRPD1a，RNA依赖的RNA聚合酶2(RDR2)和DICER-LIKE 3(DCL3)，是接收长距离mRNA沉默所必需的。代表该途径中第四个基因的突变体ARGONAUTE4(Ago4)也在接受沉默的过程中部分受损。这一途径产生24-nT的siRNAs，并导致解帽RNA，这是RDR6扩增dsRNA的已知底物。嫁接芽中沉默的激活依赖于RDR6，但在突变体rdr6中没有检测到24个核苷酸的siRNAs，这表明RDR6也在最初的信号感知中发挥作用。在扩增截断的转录本后，DCL4和DCL2就像它们在抗病毒抗性中所做的那样分级地发挥作用，分别产生21和22个核苷酸的siRNAs，这些siRNAs引导mRNA降解。还测试了几个DCL基因型传递来自砧木的移动沉默信号的能力。Dcl1-8和dcl2、dcl3、dcl4三个突变体分别在microRNA和siRNA的生物发生中受到影响，但在信号传递方面没有受到影响。
In plants, silencing of mRNA can be transmitted from cell to cell and also over longer distances from roots to shoots. To investigate the long-distance mechanism, WT and mutant shoots were grafted onto roots silenced for an mRNA. We show that three genes involved in a chromatin silencing pathway, NRPD1a encoding RNA polymerase IVa, RNA-dependent RNA polymerase 2 (RDR2), and DICER-like 3 (DCL3), are required for reception of long-distance mRNA silencing in the shoot. A mutant representing a fourth gene in the pathway, argonaute4 (ago4), was also partially compromised in the reception of silencing. This pathway produces 24-nt siRNAs and resulted in decapped RNA, a known substrate for amplification of dsRNA by RDR6. Activation of silencing in grafted shoots depended on RDR6, but no 24-nt siRNAs were detected in mutant rdr6 shoots, indicating that RDR6 also plays a role in initial signal perception. After amplification of decapped transcripts, DCL4 and DCL2 act hierarchically as they do in antiviral resistance to produce 21- and 22-nt siRNAs, respectively, and these guide mRNA degradation. Several dcl genotypes were also tested for their capacity to transmit the mobile silencing signal from the rootstock. dcl1-8 and a dcl2 dcl3 dcl4 triple mutant are compromised in micro-RNA and siRNA biogenesis, respectively, but were unaffected in signal transmission.