Abstract：
Ionic and metal toxicity in plants is still a global problem for the environment, agricultural productivity and ultimately poses human health threats when these metal ions accumulate in edible organs of plants. Metal and ion transport from cytosol to the vacuole is considered an important component of metal and ion tolerance and a plant\'s potential utility in phytoremediation. Finger millet (Eleusine coracana) is an orphan crop but has prominent nutritional value in comparison to other cereals. Previous transcriptomic studies suggested that one of the calcium/proton exchanger (EcCAX3) is strongly upregulated during different developmental stages of spikes development in plant. This finding led us to speculate that high calcium accumulation in the grain might be because of CAX3 function. Moreover, phylogenetic analysis shows that EcCAX3 is more closely related to foxtail millet, sorghum and rice CAX3 protein. To decipher the functional role of EcCAX3, we have adopted complementation of yeast triple mutant K677 (Δpmc1Δvcx1Δcnb1), which has defective calcium transport machinery. Furthermore, metal tolerance assay shows that EcCAX3 expression conferred tolerance to different metal stresses in yeast. The gain-of-function study suggests that EcCAX3 overexpressing Arabidopsis plants shows better tolerance to higher concentration of different metal ions as compared to wild type Col-0 plants. EcCAX3-overexpression transgenic lines exhibits abundance of metal transporters and cation exchanger transporter transcripts under metal stress conditions. Furthermore, EcCAX3-overexpression lines have higher accumulation of macro- and micro-elements under different metal stress. Overall, this finding highlights the functional role of EcCAX3 in the regulation of metal and ion homeostasis and this could be potentially utilized to engineer metal fortification and generation of stress tolerant crops in near future.
摘要：
植物中的离子和金属毒性仍然是一个全球性的环境问题，当这些金属离子在植物的可食用器官中积累时，农业生产力最终会对人类健康构成威胁。从细胞质到液泡的金属和离子运输被认为是金属和离子耐受性的重要组成部分，也是植物在植物修复中的潜在用途。小米（Eleusinecoracana）是一种孤儿作物，但与其他谷物相比具有突出的营养价值。先前的转录组学研究表明，在植物穗发育的不同发育阶段，钙/质子交换剂（EcCAX3）之一被强烈上调。这一发现使我们推测谷物中的高钙积累可能是由于CAX3功能。此外，系统发育分析表明,EcCAX3与谷子关系更为密切,高粱和大米CAX3蛋白。为了破译EcCAX3的功能作用，我们采用了酵母三重突变体K677（Δpmc1Δvcx1Δcnb1）的互补，有缺陷的钙运输机械。此外，金属耐受性分析表明，EcCAX3的表达赋予了酵母对不同金属胁迫的耐受性。功能获得研究表明，与野生型Col-0植物相比，过表达EcCAX3的拟南芥植物对更高浓度的不同金属离子表现出更好的耐受性。EcCAX3过表达转基因品系在金属胁迫条件下表现出丰富的金属转运蛋白和阳离子交换转运蛋白转录本。此外，EcCAX3过表达品系在不同金属胁迫下具有较高的宏观和微量元素积累。总的来说,这一发现强调了EcCAX3在调节金属和离子稳态中的功能作用，这可能在不久的将来被用来设计金属强化和产生耐胁迫作物。
