Cadmium (Cd) accumulation in rice grain is of health concern. Identifying genes involved in grain Cd accumulation and performing molecular breeding may reduce it. In this study, knockout of OsNRAMP2, a member of the NRAMP family, reduced grain Cd concentrations by more than 38%, and overexpressing OsNRAMP2 increased grain Cd concentrations by more than 50%. Physiological experiments showed that OsNRAMP2 facilitated Cd translocation from root to shoot by positively regulating Cd efflux from the vacuoles. At filling stage, OsNRAMP2 was highly expressed in all tissues except for husk, suggesting its role in Cd remobilization. Changes in OsNRAMP2 expression affected the concentrations of Fe, Mn, Zn, and Cu in grain and also affected rice growth. Phylogenetic analysis showed that the distribution of OsNRAMP2 haplotypes between japonica and indica was different. Among the four haplotypes of OsNRAMP2, Hap 1, with a 6-bp nucleotide insertion in exon 1, had grain Cd concentration at least 45.3% lower than any of the other three haplotypes. Almost all (99.3%) japonica accessions but rare indica accessions (4.44%) from the 3K sequenced rice genomes carry Hap 1 of OsNRAMP2. Our study sheds light on the molecular mechanism of grain Cd accumulation and provides a promising target for low-Cd rice breeding.

Rice with panicle-blast resistance is needed for stable rice production. Although we have previously demonstrated that OsGF14b underlies a quantitative trait locus that positively regulates rice panicle blast resistance, the mechanism is still unknown. In this study, a multi-omics approach was used to investigate the possible downstream signaling pathway regulated by OsGF14b. OsGF14b both strongly activated the gibberellin biosynthetic pathway during pathogen infection and reprogrammed the lignin biosynthetic pathway. Reduced lignin accumulation was observed in glumes of OsGF14b-overexpressing plants in comparison with the wild type after pathogen inoculation. OsGF14b activated the auxin and jasmonic acid signaling pathways, but inactivated the salicylic acid signaling pathway. Auxin and jasmonic acid appeared to act independently on OsGF14b-mediated panicle blast resistance. The roles of gibberellin, lignin, and auxin were different from their roles in leaf blast, suggesting that different mechanisms underlie leaf and panicle blast resistance in rice. This study provides a comprehensive catalog of molecular changes that could be targets for future studies of rice panicle blast resistance.

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 ℃, whereas discoloration appeared at moderately low temperatures such as 13 ℃. Chlorophyll contents in both cultivars were significantly decreased at 13 ℃, but not altered at 11 ℃. In contrast, the relative water content and relative electrolyte leakage of both cultivars decreased significantly at 11 ℃, but did not change at 13 ℃. Expression of genes associated with calcium signaling and abscisic acid (ABA) degradation was significantly altered at 11 ℃ in comparison with 25 ℃ and 13 ℃. 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 ℃ in comparison with 25 ℃ and 13 ℃. 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.