Abstract
In temperate areas, rice deals with low temperatures that can affect plant growth and crop yield. Rapid germination is required for adequate plant establishment in the field, therefore obtaining cultivars that maintain this phenotype under suboptimal temperature conditions is a challenge for rice breeders. Our study aimed to investigate temperature-induced expression changes in genes underlying quantitative trait loci (QTLs) associated to this trait (low temperature germinability, LTG) that were detected in a previous genome wide association study (GWAS). In the context of a breeding program for japonica rice cultivars adapted to cultivation in Spain, we obtained two biparental families of lines derived from hybridization with two cold tolerant Italian cultivars, and we have studied the effect on the LTG phenotype of introgressing these QTLs. A wide region in chromosome 3 was related to significant increases in seedling growth rate at 15 °C, although the extent of the effect depended on the analyzed family. In parallel, we studied the pattern of expression during germination at different temperatures of 10 genes located in the LTG-associated QTLs, in five japonica rice cultivars and in a biparental family of recombinant inbred lines (RILs). Cold induced changes in the expression of the 10 analyzed genes, with significant differences among genotypes. Variation in LTG phenotype was consistently associated with changes in the pattern of expression of five genes from the tagged regions in rice chromosome 3, which encoded for enzymes implicated in phytohormone metabolism (OsFBK12, Os3Bglu6), oxidative stress (SPL35, OsSRO1c) and Mn homeostasis maintenance (OsMTP8.1). Differential expression induced by cold in two regulatory genes (Os02g0824000 and Os06g06400) also contributed to explain low temperature tolerance during rice germination. In conclusion, introgression in defective cultivars of favorable alleles for these genes would contribute to the genetic improvement of LTG in japonica rice varieties.
Highlights
Different cultivation systems and plant adaptation strategies have allowed rice (Oryza sativa L.) crops to expand worldwide, from its tropical region of origin in Southern Asia to temperate zones in North America and Europe
Our study aimed to investigate temperature-induced expression changes in genes underlying quantitative trait loci (QTLs) associated to this trait that were detected in a previous genome wide association study (GWAS)
In the context of a breeding program for japonica rice cultivars adapted to cultivation in Spain, we obtained two biparental families of lines derived from hybridization with two cold tolerant Italian cultivars, and we have studied the effect on the low temperature tolerance at germination (LTG) phenotype of introgressing these QTLs
Summary
Different cultivation systems and plant adaptation strategies have allowed rice (Oryza sativa L.) crops to expand worldwide, from its tropical region of origin in Southern Asia to temperate zones in North America and Europe. In the European Union, rice is cultivated from about 450,000 ha, mainly in Italy and Spain, and in Greece, Portugal, and France, with a mean yield of 7 t/ha. In these countries, rice crops are usually located in soils with salinity and flooding problems, in or near wetlands under high environmental protection. Temperate japonica varieties progressively adapted to colder climates with shorter growing seasons by flowering under long day conditions [4]
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