Rice (Oryza sativa L.) ssp. indica is the most cultivated species in the South of Brazil. However, these plants face low temperature stress from September to November, which is the period of early sowing, affecting plant development during the initial stages of growth, and reducing rice productivity. This study aimed to characterize the root response to low temperature stress during the early vegetative stage of two rice genotypes contrasting in their cold tolerance (CT, cold-tolerant; and CS, cold-sensitive). Root dry weight and length, as well as the number of root hairs, were higher in CT than CS when exposed to cold treatment. Histochemical analyses indicated that roots of CS genotype present higher levels of lipid peroxidation and H2O2 accumulation, along with lower levels of plasma membrane integrity than CT under low temperature stress. RNAseq analyses revealed that the contrasting genotypes present completely different molecular responses to cold stress. The number of over-represented functional categories was lower in CT than CS under cold condition, suggesting that CS genotype is more impacted by low temperature stress than CT. Several genes might contribute to rice cold tolerance, including the ones related with cell wall remodeling, cytoskeleton and growth, signaling, antioxidant system, lipid metabolism, and stress response. On the other hand, high expression of the genes SRC2 (defense), root architecture associated 1 (growth), ACC oxidase, ethylene-responsive transcription factor, and cytokinin-O-glucosyltransferase 2 (hormone-related) seems to be related with cold sensibility. Since these two genotypes have a similar genetic background (sister lines), the differentially expressed genes found here can be considered candidate genes for cold tolerance and could be used in future biotechnological approaches aiming to increase rice tolerance to low temperature.

中文翻译：

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不同基因型水稻根系对低温胁迫的响应

水稻 (Oryza sativa L.) ssp。籼稻是巴西南部栽培最多的品种。然而，这些植物在 9 月至 11 月即早播期面临低温胁迫，在生长初期影响植物发育，降低水稻产量。本研究旨在表征两种水稻基因型（CT，耐寒；CS，冷敏感）在营养早期对低温胁迫的响应。当暴露于冷处理时，CT 中的根干重和长度以及根毛数量高于 CS。组织化学分析表明，在低温胁迫下，CS 基因型的根呈现出更高水平的脂质过氧化和 H2O2 积累，以及比 CT 更低水平的质膜完整性。RNAseq 分析表明，对比基因型对冷应激表现出完全不同的分子反应。在寒冷条件下，CT 中过度表达的功能类别的数量低于 CS，这表明 CS 基因型受低温胁迫的影响比 CT 更大。几个基因可能有助于水稻耐寒，包括与细胞壁重塑、细胞骨架和生长、信号传导、抗氧化系统、脂质代谢和应激反应相关的基因。另一方面，基因 SRC2（防御）、根结构相关基因 1（生长）、ACC 氧化酶、乙烯反应性转录因子和细胞分裂素-O-葡萄糖基转移酶 2（激素相关）基因的高表达似乎与感冒有关。感性。由于这两种基因型具有相似的遗传背景（姐妹系），