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

Abstract

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 °C, whereas discoloration appeared at moderately low temperatures such as 13 °C. Chlorophyll contents in both cultivars were significantly decreased at 13 °C, but not altered at 11 °C. In contrast, the relative water content and relative electrolyte leakage of both cultivars decreased significantly at 11 °C, but did not change at 13 °C. Expression of genes associated with calcium signaling and abscisic acid (ABA) degradation was significantly altered at 11 °C in comparison with 25 °C and 13 °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 °C in comparison with 25 °C and 13 °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. Keywords: Rice (Oryza sativa L.), Cold-induced leaf yellowing, Cold-induced leaf rolling, Physiological analysis, Genome-wide expression profiling