Comprehensive Transcriptomic and Physiological Insights into the Response of Root Growth Dynamics During the Germination of Diverse Sesame Varieties to Heat Stress

Heat stress constitutes a serious threat to sesame (Sesamum indicum L.). Root development during seed germination plays an essential role in plant growth and development. Nevertheless, the regulatory mechanisms underlying heat stress remain poorly understood. In this study, two sesame varieties differing in leaf heat tolerance (Zheng Taizhi 3 (heat-tolerant) and SP19 (heat-sensitive)) have been employed to investigate the impact of heat stress on root growth during germination. The results showed that heat stress significantly reduced the radicle length by 35.71% and 67.02% in Zheng Taizhi 3 and SP19, respectively, while germination rates remained unchanged. In addition, heat stress induced oxidative stress, as evidenced by increased reactive oxygen species (ROS) production, malondialdehyde (MDA) content, and reduced indole-3-acetic acid (IAA) content, accompanied by enhanced antioxidant enzyme activities, including those of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), and the abscisic acid (ABA) content significantly increased in both varieties. However, the oxidation resistance in the roots of Zheng Taizhi 3 was enhanced compared to that of SP19 under heat stress, while IAA production was maintained and ABA content was reduced. A comparative transcriptome analysis identified 6164 and 6933 differentially expressed genes (DEGs) in Zheng Taizhi 3 and SP19, respectively, with 4346 overlapping DEGs. These DEGs included those related to stress tolerance, such as heat-shock proteins (HSPs), the antioxidant defense system, hormone signal transduction, and the biosynthetic pathway of phenylpropanoid. These findings provide insights into the physiological and molecular mechanisms underlying the adaptation of sesame to heat stress, which could inform breeding strategies for developing heat-tolerant sesame varieties.