Time of day and genotype sensitivity adjust molecular responses to temperature stress in Sorghum. Time of day and genotype sensitivity adjust molecular responses to temperature stress in Sorghum

Sorghum is one of the four major C4 crops that are considered to be tolerant to environmental extremes. Sorghum shows distinct growth responses to temperature stress depending on the sensitivity of the genetic background. About half of the transcripts in sorghum exhibit diurnal rhythmic expressions emphasizing significant coordination with the environment. However, an understanding of how molecular dynamics contribute to genotype-specific stress responses in the context of the time of day is not known. We examined whether temperature stress and the time of day impact the gene expression dynamics in cold-sensitive and tolerant and heat-sensitive and tolerant sorghum genotypes. We found that time of day is highly influencing the temperature stress responses, which can be explained by the rhythmic expression of most thermo-responsive genes. This effect is more pronounced in thermo-tolerant genotypes, suggesting a stronger regulation of gene expression by the time of day and/or by the circadian clock. Genotypic differences were mostly observed on average gene expression levels, but we identified groups of genes regulated by temperature stress in a time-of-day and genotype-specific manner. These include transcriptional regulators and several members of the Ca2+-binding EF-hand protein family. We speculate that expression variation of these genes between genotypes may be responsible for contrasting sensitivities to temperature stress in tolerant vs susceptible sorghum varieties. These findings offer a new opportunity to selectively target specific genes in efforts to develop climate-resilient crops based on their time of day and genotype variation responses to temperature stress. Overall design: We performed a transcriptomic analysis from leaves that were collected in control conditions or after 1 h temperature stress (either cold or heat stress), applied at four different times of day (ZT1, ZT6, ZT9 and ZT15), in the thermo-sensitive genotype RTX430 and in tolerant genotypes (SC224 and Macia for the cold stress and heat stress experiments, respectively).

高粱是四大C4作物（C4 crop）之一，被认为具有极端环境耐受能力。高粱对温度胁迫的生长响应存在显著差异，这取决于其遗传背景的敏感性。高粱体内约半数转录本（transcripts）呈现昼夜节律性表达，凸显其与环境的高度协同性。然而，目前学界尚未明确分子动态如何在昼夜节律维度介导基因型特异性的胁迫响应。本研究探究了温度胁迫与昼夜节律是否会影响冷敏感、耐冷以及热敏感、耐热高粱基因型的基因表达动态。研究发现，昼夜节律极大地调控温度胁迫响应，这一现象可通过多数热响应基因的节律性表达得以解释。该效应在耐热/耐冷基因型中更为显著，表明昼夜节律或生物钟（circadian clock）对基因表达的调控作用更强。基因型差异主要体现在平均基因表达水平上，但本研究鉴定出了一批受温度胁迫调控、且呈现授时因子时间（Zeitgeber Time, ZT）特异性与基因型特异性调控模式的基因类群，其中包括转录调控因子（transcriptional regulators）以及多个Ca²⁺结合EF手型蛋白家族（Ca²⁺-binding EF-hand protein family）成员。我们推测，这些基因在不同基因型间的表达差异，可能是耐胁迫与敏感高粱品种间温度胁迫敏感性迥异的原因。本研究结果为基于昼夜节律和基因型对温度胁迫的响应差异，定向靶向特定基因以培育适应气候变化的作物提供了新的思路。实验总体设计：本研究对不同处理条件下的叶片样本开展转录组分析（transcriptomic analysis）：处理分为对照组与经1小时温度胁迫（冷胁迫或热胁迫）处理的样本，胁迫施加于一天中的四个授时因子时间节点（ZT1、ZT6、ZT9及ZT15）；所用实验材料包括冷敏感基因型RTX430，以及分别用于冷胁迫和热胁迫实验的耐胁迫基因型SC224与Macia。