Voorburg Corien M, Bai Yuling, Kormelink Richard
Laboratory of Virology, Department of Plant Sciences, Wageningen University and Research, Wageningen, Netherlands.
Plant Breeding, Department of Plant Sciences, Wageningen University and Research, Wageningen, Netherlands.
Front Plant Sci. 2021 Nov 18;12:757165. doi: 10.3389/fpls.2021.757165. eCollection 2021.
presents an atypical dominant resistance gene that codes for an RNA-dependent RNA polymerase (RDR) of the gamma class and confers resistance to tomato yellow leaf curl virus (TYLCV) and other geminiviruses. Tomato lines bearing not only produce relatively higher amounts of viral small interfering (vsi)RNAs, but viral DNA also exhibits a higher amount of cytosine methylation. Whether Ty-1 specifically enhances posttranscriptional gene silencing (PTGS), leading to a degradation of RNA target molecules and primarily relying on 21-22 nucleotides (nts) siRNAs, and/or transcriptional gene silencing (TGS), leading to the methylation of cytosines within DNA target sequences and relying on 24-nts siRNAs, was unknown. In this study, small RNAs were isolated from systemically TYLCV-infected leaves of encoding tomato plants and susceptible tomato Moneymaker (MM) and sequence analyzed. While in susceptible tomato plants vsiRNAs of the 21-nt size class were predominant, their amount was drastically reduced in tomato containing . The latter, instead, revealed elevated levels of vsiRNAs of the 22- and 24-nt size classes. In addition, the genomic distribution profiles of the vsiRNAs were changed in plants compared with those from susceptible MM. In MM three clear hotspots were seen, but these were less pronounced in plants, likely due to enhanced transitive silencing to neighboring viral genomic sequences. The largest increase in the amount of vsiRNAs was observed in the intergenic region and the V1 viral gene. The results suggest that Ty-1 enhances an antiviral TGS response. Whether the elevated levels of 22 nts vsiRNAs contribute to an enhanced PTGS response or an additional TGS response involving a noncanonical pathway of RNA dependent DNA methylation remains to be investigated.
呈现了一个非典型的显性抗性基因，该基因编码γ类RNA依赖的RNA聚合酶（RDR），并赋予对番茄黄化曲叶病毒（TYLCV）和其他双生病毒的抗性。携带该基因的番茄品系不仅产生相对较高量的病毒小干扰（vsi）RNA，而且病毒DNA也表现出较高水平的胞嘧啶甲基化。Ty-1是否特异性增强转录后基因沉默（PTGS），导致RNA靶分子降解且主要依赖21 - 22个核苷酸（nts）的siRNA，和/或转录基因沉默（TGS），导致DNA靶序列内的胞嘧啶甲基化且依赖24 - nts的siRNA，尚不清楚。在本研究中，从编码番茄植株和易感番茄Money maker（MM）的系统感染TYLCV的叶片中分离出小RNA并进行序列分析。在易感番茄植株中，2l - nt大小类别的vsiRNA占主导，而在含有该基因的番茄中其数量急剧减少。相反，后者显示22 - nt和24 - nt大小类别的vsiRNA水平升高。此外，与易感MM植株相比，该基因植株中vsiRNA的基因组分布图谱发生了变化。在MM植株中可看到三个明显的热点，但在该基因植株中不太明显，这可能是由于对相邻病毒基因组序列的传递性沉默增强所致。在基因间区域和V1病毒基因中观察到vsiRNA数量增加最多。结果表明Ty-1增强了抗病毒TGS反应。22 - nt vsiRNA水平的升高是否有助于增强PTGS反应或涉及RNA依赖的DNA甲基化非经典途径的额外TGS反应仍有待研究。
