1. DNA MMR系统在Cd诱导的DNA损伤修复中的作用研究
Cd是植物生长的非必需金属元素，但是可以利用其他必需元素的二价金属离子（例如Zn2+、Mn2+、Fe2+、Ca2+等）的膜蛋白转运体而被植物根系吸收[1]。Cd可直接作用于DNA碱基对的氢键，导致植物产生各种可逆或不可逆的DNA损伤，如碱基不匹配、插入/删除环、DNA加合物、DNA链交联和断裂等[2-3]。并且，Cd胁迫可以诱导植物体内产生大量的活性氧，对DNA或RNA形成氧化修饰，间接导致DNA损伤[4-5]。
DNA损伤信号能够被DNA损伤信号感受器，包括MutS、单链结合蛋白RPA （Replication protein A）复合体和MRN（MRE11-RAD50-NBS1）复合体，识别并传递，从而激活ATM/ ATR激酶，进而调控细胞周期阻滞、细胞内复制、细胞凋亡和DNA损伤修复等生物进程[6]。其中，由DNA MMR家族构成的MutS复合体（包括MutSα，MutSβ和MutSγ）是Cd胁迫引起的DNA损伤信号的主要传感器[7-9]。其中MutSα（由MSH2和MSH6蛋白构成）和MutSγ（由MSH2和MSH7蛋白构成）主要负责识别DNA序列中1-2个碱基错配，而MutSβ（由MSH2和MSH3蛋白构成）主要识别由2-12个碱基错配修复引起的插入/缺失环[9]。当DNA错配信息被识别后，MutLα（由MLH1和PSM1蛋白构成）被招募，并与结合在DNA链上的MutSα /β /γ 形成临时复合体，并通过PCNA和RFC信号通路启动DNA MMR反应[10]；同时MutLα- MutSα复合体还能够通过ATM/ ATR信号途径启动细胞周期检验点，调控细胞周期相关基因表达和细胞周期进程[8]。在拟南芥和大豆中，MSH2和MSH6作为Cd诱导的DNA损伤信号的主要传感器，参与细胞周期的G2/M期阻滞 [8-9]。DNA损伤信号引起的细胞周期阻滞，为DNA损伤的修复提供充足的时间，对维护生物体遗传信息的高保真性具有重要意义。另有研究表明，MutSα复合体中的MSH2可直接向ATR传递损伤信号，激活ATR-ATRIP途径[11-12]；MSH2也可以招募DNA修复蛋白和MutLα复合体，并将损伤信号传递并激活ATM [13-14]；活化后的ATM/ATR激活细胞周期检验点，并通过一系列的信号转导最终激活DNA损伤修复反应[15]。
2. miRNAs在植物生长发育和逆境胁迫中的调控作用研究
miRNAs是真核生物体内普遍存在的、长度为18-25个核苷酸（nt）的内源性非编码单链小分子RNA，能够与靶基因mRNA上的一些序列进行特异性的结合，诱导靶基因mRNA被剪切或抑制其翻译，从而在转录后水平上调控靶基因的表达[16] 。大量的研究结果表明，miRNA作为一种基因表达的负调控因子，参与了植物生长发育、胁迫应答、激素分泌与信号转导等多种生理代谢过程，在植物的非生物胁迫响应，特别是重金属胁迫响应中发挥了重要作用。
最新的研究表明，miRNAs也是植物之间互作的信号物质。植物体内的miRNAs还可以通过韧皮部进行长距离运输，从而发挥信号作用[17]。并且，局部应激产生的miRNAs也能够通过韧皮部运输到达植物的其它组织，发挥基因调控表达的作用。植物分泌的miRNAs能够影响相邻植株的基因表达[18]。而且，研究证明，通过局部添加外源人工合成的miRNAs（double-stranded RNAs，dsRNAs）能够激活植物体内的RNAi机制，调控整株植物内靶基因的表达[19]
随着miRNA测序和降解组分析等高通量测序技术的发展和普及，越来越多的miRNAs和其靶基因被鉴定，其在生物生理代谢及逆境胁迫响应中的作用也逐渐的被明确。并且，在人类和动物医学等相关领域，miRNAs作为肿瘤等疾病分子标记物的作用也不断被开发[20-22]。尽管如此，植物中靶向MMR系统中关键基因的miRNAs的鉴定及其在Cd胁迫响应中的作用机制研究，在国内外报道尚少。
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