Institute of Plant and Microbial Biology, Academia Sinica, Taipei 115, Taiwan.
Department of Biology, Pennsylvania State University, University Park, Pennsylvania 16802.
Plant Physiol. 2019 Apr;179(4):1620-1631. doi: 10.1104/pp.18.01185. Epub 2019 Feb 1.
The stress hormone abscisic acid (ABA) is critical for drought resistance; however, mechanisms controlling ABA levels are unclear. At low water potential, ABA accumulation in the Arabidopsis () accession Shahdara (Sha) was less than that in Landsberg (L) or Columbia. Analysis of a L × Sha recombinant inbred line population revealed a single major-effect quantitative trait locus for ABA accumulation, which included () as a candidate gene. encodes a rate-limiting enzyme for stress-induced ABA synthesis. Complementation experiments indicated that Sha has a reduced-function allele. Compared with L, Sha did not have reduced gene expression or protein level but did have four amino acid substitutions within NCED3. Sha differed from L in the apparent molecular mass of NCED3, indicative of altered NCED3 proteolytic processing in the chloroplast. Site-directed mutagenesis demonstrated that substitution at amino acid 271 was critical for the altered NCED3 molecular mass pattern, while the other Sha NCED3 polymorphisms were also involved in the reduced ABA accumulation. Sha did not have a reduced level of thylakoid-bound NCED3 but did differ from L in the apparent molecular mass of stromal NCED3. As Sha was not impaired in known factors critical for NCED3 function in ABA synthesis (expression, chloroplast import, and thylakoid binding), the differences between L and Sha NCED3 may affect NCED3 activity or other factors influencing NCED3 function. These results identify functionally important sites on NCED3 and indicate a complex pattern of NCED3 posttranslational regulation in the chloroplast.
胁迫激素脱落酸（ABA）对于抗旱性至关重要；然而，控制 ABA 水平的机制尚不清楚。在低水势下，拟南芥（）品系 Shahdara（Sha）中的 ABA 积累量低于 Landsberg （L）或 Columbia。对 L × Sha 重组自交系群体的分析揭示了一个单一的主要效应数量性状位点，用于 ABA 积累，其中包含（）作为候选基因。编码应激诱导 ABA 合成的限速酶。互补实验表明 Sha 具有功能降低的 等位基因。与 L 相比，Sha 的 基因表达或蛋白水平没有降低，但在 NCED3 内确实有四个氨基酸取代。Sha 在 NCED3 的表观分子量与 L 不同，表明 NCED3 在叶绿体中的蛋白水解加工发生了改变。定点突变表明，氨基酸 271 的取代对于改变的 NCED3 分子量模式至关重要，而 Sha 的其他 NCED3 多态性也参与了减少的 ABA 积累。Sha 没有减少类囊体结合的 NCED3 水平，但在基质 NCED3 的表观分子量上与 L 不同。由于 Sha 在 NCED3 功能（表达、叶绿体导入和类囊体结合）的已知关键因素方面没有受损，因此 L 和 Sha NCED3 之间的差异可能影响 NCED3 活性或影响 NCED3 功能的其他因素。这些结果确定了 NCED3 上具有功能重要性的位点，并表明了 NCED3 在叶绿体中复杂的翻译后调控模式。
