Chlorophyll (Chl) loss is one of the most visible symptoms of heat-induced leaf senescence, especially for cool-season grass species. Suppression of the Chl a Me-dechelatase gene, SGR (also named as nye1), blocked the degradation of Chl a and resulted in the ‘stay-green’ trait during leaf senescence. However, effect of Chl a catabolism on plant tolerance to long-term moderate heat stress (35-40°C) remains unclear. In this study, we suppressed the expression of Chl a catabolic gene, LpSGR, in both constitutive and inducible manners in perennial ryegrass. Constitutive suppression of LpSGR aggravated heat stress-induced chloroplast structure and photosystem damages, disrupted energy utilization/dissipation during photosynthesis, activated ROS generation with weakened ROS-scavenging enzyme activities. Transcriptome comparison among wildtype (WT) and transgenic RNAi plants under either the optimum or high temperature conditions also emphasized the effect of Chl a catabolism on expression of genes encoding photosynthesis system, ROS-generation and scavenging system, and heat shock transcription factors. Furthermore, making use of a modified ethanol-inducible system, we generated stable transgenic perennial ryegrass to suppress LpSGR in an inducible manner. Without ethanol induction, these transgenic lines exhibited the same growth and heat tolerance traits to WT, while under the induction of ethanol spray, the transgenic lines also showed compromised heat tolerance. Taken together, our data suggest that Chl a catabolism is critical for energy dissipation and electron transfer in photosynthesis, ROS-balancing and chloroplast membrane system stability upon long-term moderate heat stress.

中文翻译：

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STAYGREEN 介导的叶绿素 a 分解代谢对黑麦草热应激下的光系统稳定性至关重要

叶绿素 (Chl) 损失是热诱导的叶子衰老最明显的症状之一，尤其是对于冷季草种。Chl a Me-去螯合酶基因SGR（也称为nye1）的抑制阻止了Chl a 的降解并导致叶子衰老期间的“保持绿色”性状。然而，Chl a 分解代谢对植物对长期中等热应激（35-40°C）的耐受性的影响仍不清楚。在这项研究中，我们在多年生黑麦草中以组成型和诱导型两种方式抑制 Chl 分解代谢基因LpSGR的表达。LpSGR 的组成性抑制加剧热应激诱导的叶绿体结构和光系统损伤，破坏光合作用过程中的能量利用/耗散，激活 ROS 生成，同时减弱 ROS 清除酶活性。在最佳或高温条件下野生型 (WT) 和转基因 RNAi 植物之间的转录组比较也强调了 Chl a 分解代谢对编码光合作用系统、ROS 生成和清除系统以及热休克转录因子的基因表达的影响。此外，利用改良的乙醇诱导系统，我们产生了稳定的转基因多年生黑麦草来抑制LpSGR以诱导方式。在没有乙醇诱导的情况下，这些转基因品系表现出与 WT 相同的生长和耐热性状，而在乙醇喷雾诱导下，转基因品系的耐热性也有所下降。总之，我们的数据表明 Chl a 分解代谢对于光合作用中的能量耗散和电子转移、ROS 平衡和叶绿体膜系统在长期中等热应激下的稳定性至关重要。