水稻吸铵基因OsAMT12和OsAMT33在不同生育期中的表达量差异及其在酵母细胞中吸铵功能初析

本文利用定量PCR技术分析了OsAMT1.2和OsAMT3.3在水稻根中的表达水平,并应用铵吸收功能缺陷型酵母突变体分析OsAMT1.2和OsAMT3.3对NH4+ 的转运功能及影响基因功能异源表达的可能因素.结果表明,OsAMT1.2和OsAMT3.3在分蘖期的表达水平较苗期高;苗期OsAMT1.2与OsAMT3.3的转录水平差异不显著,但分蘖期OsAMT1.2的表达水平快速升高,较苗期提高了5倍,而OsAMT3.3的表达量只提高了一倍,导致两者的表达水平存在显著差异.缺N处理2天两基因均有被诱导增强表达的趋势,其中苗期的增加幅度明显高于分蘖期.当外源供给1mmol/L NH4+,OsAMT1.2在铵吸收功能缺陷型酵母突变体上仅表现部分功能,而OsAMT3.3则不能实现吸铵功能互补.以AtAMT1.1为对照,分析OsAMT1.2在酵母中的表达水平,结果表明异源系统中OsAMT1.2的相对表达量仅有AtAMT1.1的50%.本文的结果说明,外源基因在酵母异源系统中的异源表达,除了与基因产物本身的功能有关,还取决于宿主酵母细胞对其表达水平的调控,因而表现出受内源机制调控的特征.

Expression of OsAMT12 and OsAMT33 in rice root with relation to different growth stages and functional characterization in yeast mutant

Two cDNAs encoding respectively, OsAMT1.2 and OsAMT3.3, were isolated from rice cultivars Guidan 4. The expressions of both genes in the roots of rice seedlings were induced significantly under nitrogen starvation. A yeast mutant deficient in ammonium (NH4+) transport was employed to elucidate their functional aspects. Expression of OsAMT1.2 in the yeast mutant partially complemented NH4+ uptake deficiency of the mutant cells, while OsAMT3.3 did not confer functional complementation. Relative gene expression analysis in yeast revealed a 50% lower abundance of OsAMT1.2 mRNA than the Arabidopsis AtAMT1.1, a functional NH4+ transporter characterized in the same system. Thus, the low abundant expression in the yeast system may be one of the reasons that the OsAMTs was not consequently capable for functional complementation. Our results give a clue to the consideration of using yeast for functional characterization of foreign genes in such heterologous system.