Plant Molecular Biology Laboratory, M. S. Swaminathan Research Foundation, III Cross Street, Taramani Institutional Area, Chennai, 600113, India.
Tasmanian Institute of Agriculture, College of Science and Engineering, University of Tasmania, Private Bag 98, Hobart, Tas, 7001, Australia; International Research Centre for Environmental Membrane Biology, Foshan University, Foshan, 528000, China.
Plant Physiol Biochem. 2021 Dec;169:333-342. doi: 10.1016/j.plaphy.2021.11.030. Epub 2021 Nov 19.
Arid/semi-arid and coastal agricultural areas of the world are especially vulnerable to climate change-driven soil salinity. Salinity tolerance in plants is a complex trait, with salinity negatively affecting crop yield. Plants adopt a range of mechanisms to combat salinity, with many transporter genes being implicated in Na-partitioning processes. Within these, the high-affinity K (HKT) family of transporters play a critical role in K and Na homeostasis in plants. Among HKT transporters, Type I transporters are Na-specific. While Arabidopsis has only one Na -specific HKT (AtHKT1;1), cereal crops have a multiplicity of Type I and II HKT transporters. AtHKT1; 1 (Arabidopsis thaliana) and HKT1; 5 (cereal crops) 'exclude' Na from the xylem into xylem parenchyma in the root, reducing shoot Na and hence, confer sodium tolerance. However, more recent data from Arabidopsis and crop species show that AtHKT1;1/HKT1;5 alleles have a strong genetic association with 'shoot sodium accumulation' and concomitant salt tolerance. The review tries to resolve these two seemingly contradictory effects of AtHKT1;1/HKT1;5 operation (shoot exclusion vs shoot accumulation), both conferring salinity tolerance and suggests that contrasting phenotypes are attributable to either hyper-functional or weak AtHKT1;1/HKT1;5 alleles/haplotypes and are under strong selection by soil salinity levels. It also suggests that opposite balancing mechanisms involving xylem ion loading in these contrasting phenotypes exist that require transporters such as SOS1 and CCC. While HKT1; 5 is a crucial but not sole determinant of salinity tolerance, investigation of the adaptive benefit(s) conferred by naturally occurring intermediate HKT1;5 alleles will be important under a climate change scenario.
世界上的干旱/半干旱和沿海农业区特别容易受到气候变化导致的土壤盐渍化的影响。植物的耐盐性是一个复杂的特性，盐度会对作物产量产生负面影响。植物采用了一系列机制来对抗盐度，许多转运蛋白基因与 Na 分配过程有关。在这些基因中，高亲和力 K（HKT）转运蛋白家族在植物的 K 和 Na 稳态中起着关键作用。在 HKT 转运蛋白中，I 型转运蛋白是 Na 特异性的。虽然拟南芥只有一个 Na 特异性 HKT（AtHKT1;1），但谷类作物有多种 I 型和 II 型 HKT 转运蛋白。AtHKT1;1（拟南芥）和 HKT1;5（谷类作物）“将 Na 从木质部排除到根部的木质部薄壁组织中，减少地上部的 Na，从而赋予耐钠性。然而，来自拟南芥和作物物种的最新数据表明，AtHKT1;1/HKT1;5 等位基因与“地上部 Na 积累”和伴随的耐盐性有很强的遗传关联。该综述试图解决 AtHKT1;1/HKT1;5 作用（地上部排除与地上部积累）这两个看似矛盾的效应，这两个效应都赋予了耐盐性，并表明相反的表型归因于 AtHKT1;1/HKT1;5 等位基因/单倍型的超功能或弱功能，并且受到土壤盐度水平的强烈选择。它还表明，在这些相反的表型中存在涉及木质部离子加载的相反的平衡机制，这些机制需要 SOS1 和 CCC 等转运蛋白。虽然 HKT1;5 是耐盐性的关键但不是唯一决定因素，但在气候变化情景下，研究自然存在的中间 HKT1;5 等位基因赋予的适应性益处将是重要的。
