College of Biological and Pharmaceutical, China Three Gorges University, Yichang, 443002, China.
School of Life Science and Biotechnology, Wuhan University of Bioengineering, Wuhan, 430415, China.
BMC Plant Biol. 2023 Mar 27;23(1):163. doi: 10.1186/s12870-023-04167-1.
Cyanide is a toxic chemical that inhibits cellular respiration. In plants, cyanide can be produced by themselves, especially under stressful conditions. Cyanoalanine synthase (CAS) is a key enzyme involved in plant cyanide detoxification. There are three genes encoding CAS in Arabidopsis thaliana, but the roles of these genes in the plant's response to stress are less studied. In addition, it is known that alternative oxidase (AOX) mediates cyanide-resistant respiration, but the relationship between CAS and AOX in regulating the plant stress response remains largely unknown.
Here, the effects of the overexpression or mutation of these three CAS genes on salt stress tolerance were investigated. The results showed that under normal conditions, the overexpression or mutation of the CAS genes had no significant effect on the seed germination and growth of Arabidopsis thaliana compared with wild type (WT). However, under 50, 100, and 200 mM NaCl conditions, the seeds overexpressing CAS genes showed stronger salt stress resistance, i.e., higher germination speed than WT seeds, especially those that overexpressed the CYS-C1 and CYS-D1 genes. In contrast, the seeds with CAS gene mutations exhibited salt sensitivity, and their germination ability and growth were significantly damaged by 100 and 200 mM NaCl. Importantly, this difference in salt stress resistance became more pronounced in CAS-OE, WT, and mutant seeds with increasing salt concentration. The CAS-OE seeds maintained higher respiration rates than the WT and CAS mutant seeds under salt stress conditions. The cyanide contents in CAS mutant seeds were approximately 3 times higher than those in WT seeds and more than 5 times higher than those in CAS-OE seeds. In comparison, plants overexpressing CYS-C1 had the fastest detoxification of cyanide and the best salt tolerance, followed by those overexpressing CYS-D1 and CYS-D2. Furthermore, less hydrogen sulfide (HS) was observed in CAS-OE seedlings than in WT seedlings under long-term salt stress conditions. Nonetheless, the lack of AOX impaired CAS-OE-mediated plant salt stress resistance, suggesting that CAS and AOX interact to improve salt tolerance is essential. The results also showed that CAS and AOX contributed to the reduction in oxidative damage by helping maintain relatively high levels of antioxidant enzyme activity.
In summary, the findings of the present study suggest that overexpression of Arabidopsis CAS family genes plays a positive role in salt stress tolerance and highlights the contribution of AOX to CAS-mediated plant salt resistance, mainly by reducing cyanide and HS toxicity.
氰化物是一种抑制细胞呼吸的有毒化学物质。在植物中，氰化物可以由自身产生，尤其是在应激条件下。氰酸合酶（CAS）是一种参与植物氰化物解毒的关键酶。拟南芥中有三个基因编码 CAS，但这些基因在植物应对应激反应中的作用研究较少。此外，已知交替氧化酶（AOX）介导氰化物抗性呼吸，但 CAS 和 AOX 调节植物应激反应的关系在很大程度上仍不清楚。
本研究探讨了这三个 CAS 基因的过表达或突变对盐胁迫耐受性的影响。结果表明，在正常条件下，与野生型（WT）相比，CAS 基因的过表达或突变对拟南芥种子的萌发和生长没有显著影响。然而，在 50、100 和 200mM NaCl 条件下，过表达 CAS 基因的种子表现出更强的盐胁迫抗性，即比 WT 种子更快的萌发速度，特别是过表达 CYS-C1 和 CYS-D1 基因的种子。相比之下，CAS 基因突变的种子表现出盐敏感性，其萌发能力和生长在 100 和 200mM NaCl 下受到严重损害。重要的是，随着盐浓度的增加，这种盐胁迫抗性的差异在 CAS-OE、WT 和突变种子中变得更加明显。在盐胁迫条件下，CAS-OE 种子的呼吸速率保持高于 WT 和 CAS 突变种子。CAS 突变种子中的氰化物含量比 WT 种子高约 3 倍，比 CAS-OE 种子高 5 倍以上。相比之下，过表达 CYS-C1 的植物氰化物解毒最快，耐盐性最好，其次是过表达 CYS-D1 和 CYS-D2 的植物。此外，在长期盐胁迫条件下，CAS-OE 幼苗中观察到的硫化氢（HS）较少。然而，AOX 的缺乏削弱了 CAS-OE 介导的植物耐盐性，表明 CAS 和 AOX 相互作用对提高耐盐性至关重要。结果还表明，CAS 和 AOX 通过帮助维持相对较高的抗氧化酶活性水平，有助于减少氧化损伤。
综上所述，本研究结果表明，拟南芥 CAS 家族基因的过表达在盐胁迫耐受性中发挥积极作用，并强调了 AOX 对 CAS 介导的植物耐盐性的贡献，主要是通过降低氰化物和 HS 的毒性。
