Rice RAD51 Paralogs Play Essential Roles in Somatic Homologous Recombination in DNA repair

First author: Zhan Xu; Affiliations: Yangzhou University (扬州大学): Yangzhou, China

Corresponding author: Hengxiu Yu (于恒秀)

Synthesis‐dependent strand annealing (SDSA; 合成依赖性链退火) and single‐strand annealing (SSA; 单链退火) are the two main homologous recombination (HR) pathways in double‐strand break (DSB) repair (双链断裂修复). The involvement of rice RAD51 paralogs in HR is well known in meiosis (减数分裂), although the molecular mechanism in somatic HR remains obscure. Loss‐of‐function mutants of rad51 paralogs show increased sensitivity to the DSB‐inducer bleomycin (博来霉素), which results in greatly compromised somatic recombination efficiencies (xrcc3 in SDSA, rad51b and xrcc2 in SSA, rad51c and rad51d in both). Using immunostaining (免疫染色), we found that mutations in RAD51 paralogs (XRCC3, RAD51C, or RAD51D) lead to tremendous (极大的) impairment (损伤) in RAD51 focus formation at DSBs. Intriguingly, mutation of RAD51C has a strong impact on the protein loading of its partners (XRCC3 and RAD51B) at DSBs, which is similar to the phenomenon observed in the case of blocking PI3K‐like kinases in wild‐ ype plant. We conclude that the rice CDX3 complex acts in the SDSA recombination while the BCDX2 complex acts in the SSA recombination in somatic DSB repair. Importantly, RAD51C serves as a fulcrum (支点) for the local recruitment of its partners (XRCC3 for SDSA and RAD51B for SSA), and is positively modulated by PI3K‐like kinases, to facilitate both the SDSA and SSA pathways in RAD51 paralog‐dependent somatic HR.

合成依赖性链退火SDSA和单链退火SSA是双链断裂修复中两个主要的同源重组HR通路。已知RAD51旁系同源基因在减数分裂HR中发挥重要作用，然而其在体细胞HR中的分子机制有待研究。rad51同源基因功能缺失突变会减少植株对于DSB诱导剂博来霉素的敏感性，严重损伤体细胞的重组效率，其中xrcc3突变主要影响SDSA，rad51b和xrcc2突变主要影响SSA，而rad51c和rad51d突变则同时影响SDSA和SSA。利用免疫染色，作者发现RAD51旁系同源基因XRCC3、RAD51C或者RAD51D突变会导致RAD51位点双链断裂修复出现重大缺陷。有趣的是，RAD51C突变会影响双链断裂处XRCC3和RAD51B蛋白的装载，这与野生型中阻断类PI3K激酶所观测到的现象一致。作者推测在水稻体细胞的双链断裂修复中，CDX3复合物主要作用于SDSA重组，而BCDX2复合物则作用于SSA重组。重要的是，RAD51C作为一个支点，招募XRCC3或者RAD51B，分别作用于SDSA和SSA，且受到类PI3K激酶的正向调控，通过依赖RAD51旁系同源基因的方式促进体细胞HR中的SDSA和SSA通路。

通讯：于恒秀 (http://nxy.yzu.edu.cn/art/2016/9/14/art_12481_390720.html)

研究方向：水稻分子细胞遗传学和基因工程育种研究等工作。

doi: https://doi.org/10.1111/tpj.13949

Journal: the plant journal

First Published date: 05 May, 2018

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