Sarma Supriya, Pandey Arun Kumar, Sharma Kapil, Ravi Maruthachalam, Sreelakshmi Yellamaraju, Sharma Rameshwar
Repository of Tomato Genomics Resources Department of Plant Sciences School of Life Sciences University of Hyderabad Hyderabad India.
Present address: Centre for Cellular and Molecular Biology Hyderabad India.
Plant Direct. 2018 Jan 2;2(1):e00017. doi: 10.1002/pld3.17. eCollection 2018 Jan.
MSH2 is the core protein of MutS-homolog family involved in recognition and repair of the errors in the DNA. While other members of MutS-homolog family reportedly regulate mitochondrial stability, meiosis, and fertility, MSH2 is believed to participate mainly in mismatch repair. The search for polymorphism in sequence in tomato accessions revealed both synonymous and nonsynonymous SNPs; however, SIFT algorithm predicted that none of the SNPs influenced MSH2 protein function. The silencing of gene expression by RNAi led to phenotypic abnormalities in highly silenced lines, particularly in the stamens with highly reduced pollen formation. silencing exacerbated formation of UV-B-induced thymine dimers and blocked light-induced repair of the dimers. The silencing also affected the progression of male meiosis to a varying degree with either halt of meiosis at zygotene stage or formation of diploid tetrads. The immunostaining of male meiocytes with centromere localized CENPC (centromere protein C) antibody showed the presence of 48 univalent along with 24 bivalent chromosomes suggesting abnormal tetraploid meiosis. The mitotic cells of root tips of silenced lines showed diploid nuclei but lacked intervening cell plates leading to cells with syncytial nuclei. Thus, we speculate that tetraploid pollen mother cells may have arisen due to the fusion of syncytial nuclei before the onset of meiosis. It is likely that in addition to mismatch repair (MMR), MSH2 may have an additional role in regulating ploidy stability.
MSH2是MutS同源家族的核心蛋白，参与DNA错误的识别与修复。虽然据报道MutS同源家族的其他成员调节线粒体稳定性、减数分裂和生育力，但MSH2主要被认为参与错配修复。对番茄种质序列多态性的研究揭示了同义单核苷酸多态性（SNP）和非同义SNP；然而，SIFT算法预测这些SNP均不影响MSH2蛋白功能。RNA干扰导致基因表达沉默，在高度沉默的株系中产生了表型异常，特别是在花粉形成高度减少的雄蕊中。沉默加剧了UV-B诱导的胸腺嘧啶二聚体的形成，并阻断了二聚体的光诱导修复。沉默还在不同程度上影响了雄配子减数分裂的进程，减数分裂要么在偶线期停止，要么形成二倍体四分体。用着丝粒定位的CENPC（着丝粒蛋白C）抗体对雄配子母细胞进行免疫染色，结果显示存在48条单价染色体和24条二价染色体，表明四倍体减数分裂异常。沉默株系根尖的有丝分裂细胞显示为二倍体细胞核，但缺乏中间的细胞板，导致细胞具有合胞体细胞核。因此，我们推测四倍体花粉母细胞可能是由于减数分裂开始前合胞体细胞核的融合而产生的。除错配修复（MMR）外，MSH2可能在调节倍性稳定性方面还具有额外作用。
