Cao Min-Jie, Wang Zhen, Zhao Qing, Mao Jie-Li, Speiser Anna, Wirtz Markus, Hell Rüdiger, Zhu Jian-Kang, Xiang Cheng-Bin
School of Life Sciences, University of Science and Technology of China, Hefei, Anhui Province, 230027, China.
Plant J. 2014 Feb;77(4):604-15. doi: 10.1111/tpj.12407. Epub 2014 Jan 21.
Sulfur-containing compounds play a critical role in the response of plants to abiotic stress factors including drought. The phytohormone abscisic acid (ABA) is the key regulator of responses to drought and high-salt stress. However, our knowledge about interaction of S-metabolism and ABA biosynthesis is scarce. Here we report that sulfate supply affects synthesis and steady-state levels of ABA in Arabidopsis wild-type seedlings. By using different mutants of the sulfate uptake and reduction pathway, we confirmed the impact of sulfate supply on steady-state ABA content in Arabidopsis and demonstrated that this impact was due to cysteine availability. Loss of the chloroplast sulfate transporter3;1 function (sultr3;1) resulted in significantly decreased aldehyde oxidase (AO) activity and ABA levels in seedlings and seeds. These mutant phenotypes could be reverted by exogenous application of cysteine or ectopic expression of SULTR3;1. In addition the sultr3;1 mutant showed a decrease of xanthine dehydrogenase activity, but not of nitrate reductase, strongly indicating that in seedlings cysteine availability limits activity of the molybdenum co-factor sulfurase, ABA3, which requires cysteine as the S-donor for sulfuration. Transcription of ABA3 and NCED3, encoding another key enzyme of the ABA biosynthesis pathway, was regulated by S-supply in wild-type seedlings. In contrast, ABA up-regulated the transcript level of SULTR3;1 and other S-metabolism-related genes. Our results provide evidence for a significant co-regulation of S-metabolism and ABA biosynthesis that operates to ensure sufficient cysteine for AO maturation and highlights the importance of sulfur for stress tolerance of plants.
含硫化合物在植物对包括干旱在内的非生物胁迫因子的响应中起着关键作用。植物激素脱落酸（ABA）是对干旱和高盐胁迫响应的关键调节因子。然而，我们对硫代谢与ABA生物合成相互作用的了解却很少。在此我们报告，硫酸盐供应会影响拟南芥野生型幼苗中ABA的合成和稳态水平。通过使用硫酸盐吸收和还原途径的不同突变体，我们证实了硫酸盐供应对拟南芥中ABA稳态含量的影响，并证明这种影响是由于半胱氨酸的可用性。叶绿体硫酸盐转运蛋白3;1（SULTR3;1）功能丧失导致幼苗和种子中的醛氧化酶（AO）活性和ABA水平显著降低。这些突变表型可通过外源施用半胱氨酸或SULTR3;1的异位表达得以恢复。此外，sultr3;1突变体显示黄嘌呤脱氢酶活性降低，但硝酸还原酶活性未降低，这强烈表明在幼苗中半胱氨酸的可用性限制了钼辅因子硫化酶ABA3的活性，ABA3需要半胱氨酸作为硫化的硫供体。ABA生物合成途径中另一种关键酶的编码基因ABA3和NCED3的转录在野生型幼苗中受硫供应调节。相反，ABA上调了SULTR3;1和其他硫代谢相关基因的转录水平。我们的结果为硫代谢和ABA生物合成的显著协同调节提供了证据，这种协同调节作用是为了确保有足够的半胱氨酸用于AO成熟，并突出了硫对植物胁迫耐受性的重要性。
