Physiological and genome-wide gene expression analyses of cold-induced leaf rolling at the seedling stage in rice (Oryza sativa L.)

Leaf rolling and discoloration are two chilling-injury symptoms that are widely used as indicators for the evaluation of cold tolerance at the seedling stage in rice. However, the difference in cold-response mechanisms underlying these two traits remains unknown. In the present study, a cold-tolerant rice cultivar, Lijiangxintuanheigu, and a cold-sensitive cultivar, Sanhuangzhan-2, were subjected to low-temperature treatments and physiological and genome-wide gene expression analyses were conducted. Leaf rolling occurred at temperatures lower than 11 degrees C, whereas discoloration appeared at moderately low temperatures such as 13 degrees C. Chlorophyll contents in both cultivars were significantly decreased at 13 degrees C, but not altered at 11 degrees C. In contrast, the relative water content and relative electrolyte leakage of both cultivars decreased significantly at 11 degrees C, but did not change at 13 degrees C. Expression of genes associated with calcium signaling and abscisic acid (ABA) degradation was significantly altered at 11 degrees C in comparison with 25 degrees C and 13 degrees C. Numerous genes in the DREB, MYB, bZIP, NAC, Zinc finger, bHLH, and WRKY gene families were differentially expressed. Many aquaporin genes and the key genes in trehalose and starch synthesis were down regulated at 11 degrees C in comparison with 25 degrees C and 13 degrees C. These results suggest that the two chilling injury symptoms are temperature-specific and are controlled by different mechanisms. Cold-induced leaf rolling is associated with calcium and ABA signaling pathways and is regulated by multiple transcriptional regulators. The suppression of aquaporin genes and reduced accumulation of soluble sugars under cold stress results in a reduction in cellular water potential and consequently leaf rolling. (C) 2019 Crop Science Society of China and Institute of Crop Science, CAAS. Production and hosting by Elsevier B.V. on behalf of KeAi Communications Co., Ltd.