International Centre for Genetic Engineering and Biotechnology, Aruna Asaf Ali Marg, New Delhi, India.
Plant Mol Biol. 2011 May;76(1-2):19-34. doi: 10.1007/s11103-011-9758-0. Epub 2011 Mar 2.
The eukaryotic pre-replicative complex (Pre-RC), including heterohexameric minichromosome maintenance (MCM2-7) proteins, ensures that the DNA in genome is replicated only once per cell division cycle. The MCMs provide DNA unwinding function during the DNA replication. Since MCM proteins play essential role in cell division and most likely are affected during stress conditions therefore their overexpression in plants may help in stress tolerance. But the role of MCMs in abiotic stress tolerance in plants has not been reported so far. In this study we report that: a) the MCM6 transcript is upregulated in pea plant in response to high salinity and cold stress and not with ABA, drought and heat stress; b) MCM6 overexpression driven by a constitutive cauliflower mosaic virus-35S promoter in tobacco plants confers salinity tolerance. The T(1) transgenics plants were able to grow to maturity and set normal viable seeds under continuous salinity stress, without yield penalty. It was observed that in salt-grown T(1) transgenic plants the Na(+) ions is mostly accumulated in mature leaves and not in seeds of T(1) transgenic lines as compared with the wild-type (WT) plants. T(1) transgenic plants exhibited better growth status under salinity stress conditions in comparison to WT plants. Furthermore, the T(1) transgenic plants maintained significantly higher levels of leaf chlorophyll content, net photosynthetic rate and therefore higher dry matter accumulation and yield with 200 mM NaCl as compared to the WT plants. Tolerance index data showed better salt tolerance potential of T(1) transgenic plants in comparison to WT. These findings provide first direct evidence that overexpression of single subunit MCM6 confers salinity stress tolerance without yield loss. The possible mechanism of salinity tolerance is discussed. These findings suggest that DNA replication machinery can be exploited for promoting stress tolerance in crop plants.
真核细胞复制前复合物（Pre-RC），包括异六聚体微小染色体维持（MCM2-7）蛋白，确保基因组中的 DNA 在每个细胞分裂周期中仅复制一次。MCM 在 DNA 复制过程中提供 DNA 解旋功能。由于 MCM 蛋白在细胞分裂中发挥着重要作用，并且在应激条件下很可能受到影响，因此它们在植物中的过度表达可能有助于提高对压力的耐受性。但是，到目前为止，MCM 在植物非生物胁迫耐受性中的作用尚未得到报道。在这项研究中，我们报告：a）豌豆植物中 MCM6 转录物在高盐和寒冷胁迫下上调，而不是在 ABA、干旱和热胁迫下上调；b）在烟草植物中，由组成型花椰菜花叶病毒 35S 启动子驱动的 MCM6 过表达赋予耐盐性。T(1)转基因植物能够在持续盐胁迫下成熟并产生正常有活力的种子，而不会减产。观察到，在盐生 T(1)转基因植物中，与野生型（WT）植物相比，Na(+)离子主要积累在成熟叶片中，而不是在 T(1)转基因系的种子中。T(1)转基因植物在盐胁迫条件下的生长状况优于 WT 植物。此外，与 WT 植物相比，T(1)转基因植物在 200 mM NaCl 下保持更高的叶片叶绿素含量、净光合速率，因此具有更高的干物质积累和产量。耐盐指数数据显示，与 WT 植物相比，T(1)转基因植物具有更好的耐盐潜力。这些发现首次提供了直接证据，证明单个亚基 MCM6 的过表达可在不降低产量的情况下赋予植物耐盐性。讨论了耐盐性的可能机制。这些发现表明，DNA 复制机制可用于促进作物植物的压力耐受性。
