School of Biosciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK.
J Exp Bot. 2012 Jan;63(1):59-67. doi: 10.1093/jxb/err271. Epub 2011 Oct 5.
The Arabidopsis thaliana genome encodes a family of 28 proteins whose members have been associated with the transport of monovalent cations across membranes. Experiments have been performed to elucidate the biochemical function and the role in plant development of two closely related members of this CHX family. A genotype carrying a knockout of the AtCHX23 gene (At1g05580) showed no phenotype when grown in glasshouse conditions. In particular, it did not exhibit the reduced root growth phenotype observed for a knockout of its homologue AtCHX21 when exposed to elevated sodium concentration. However, it was not possible to produce plants that were homozygous knockout for both AtCHX21 and AtCHX23. Reverse transcription-PCR (RT-PCR) experiments revealed that both genes are highly expressed in flower buds, flowers, and pollen. However, examination of pollen grain viability and pollen tube growth through excised styles did not reveal a phenotypic difference between the chx21(-)chx23(-) condition and other haplotypes. Crosses between selected mutants and wild-type plants in which the chx21(-)chx23(-) haplotype was produced by either the male or female parent demonstrated unequivocally that the chx21(-)chx23(-) haplotype could not pass through the female line. This suggests that the genes share a critical function in the development and/or function of the female gametophyte and that this function cannot be provided by other members of the AtCHX gene family. Experiments were carried out using the heterologous expression of AtCHX23 in Saccharomyces cerevisiae genotypes carrying combinations of deletions of genes involved in the transport of sodium or potassium across membranes. The results show that CHX23 would only complement the poor colony growth phenotype associated with the deletion of the yeast gene kha1. The conclusion is that both AtCHX21 and AtCHX23 act in potassium homeostasis within the female gametophyte and this is discussed in terms of the diversification of gene sequence and function within the CHX gene family.
拟南芥基因组编码了一个由 28 个蛋白组成的家族，这些蛋白成员与单离子跨膜运输有关。实验旨在阐明该 CHX 家族的两个密切相关成员的生化功能和在植物发育中的作用。在温室条件下生长时，携带 AtCHX23 基因（At1g05580）敲除突变体的基因型没有表型。特别是，当暴露于高钠浓度时，它没有表现出同源物 AtCHX21 敲除突变体观察到的根生长减少的表型。然而，不可能产生同时敲除 AtCHX21 和 AtCHX23 的纯合敲除突变体。反转录 PCR（RT-PCR）实验表明，这两个基因在花蕾、花朵和花粉中高度表达。然而，通过切除花柱检查花粉粒活力和花粉管生长并没有显示出 chx21(-)chx23(-) 条件与其他单倍型之间的表型差异。在选择的突变体和野生型植物之间进行杂交，其中 chx21(-)chx23(-) 单倍型由父本或母本产生，这明确表明 chx21(-)chx23(-) 单倍型不能通过雌性系传递。这表明这些基因在雌性配子体的发育和/或功能中具有关键作用，并且该功能不能由 AtCHX 基因家族的其他成员提供。使用 AtCHX23 在携带跨膜运输钠离子或钾离子相关基因缺失的酿酒酵母基因型中的异源表达进行了实验。结果表明，CHX23 仅能补充分离酵母基因 kha1 引起的菌落生长不良表型。结论是 AtCHX21 和 AtCHX23 在雌性配子体中的钾离子稳态中起作用，这是根据 CHX 基因家族中基因序列和功能的多样化来讨论的。
