Dissection of coleoptile elongation in japonica rice under submergence through integrated genome-wide association mapping and transcriptional analyses.

Rice is unique among cereals for its ability to germinate not only when submerged but also under anoxic conditions. Rice germination under submergence or anoxia is characterized by a longer coleoptile and delay in radicle emergence. A panel of temperate and tropical japonica rice accessions showing a large variability in coleoptile length was used to investigate genetic factors involved in this developmental process. The ability of the Khao Hlan On rice landrace to vigorously germinate when submerged has been previously associated with the presence of the trehalose 6 phosphate phosphatase 7 (TPP7) gene. In this study, we found that, in the presence of TPP7, polymorphisms and transcriptional variations of the gene in coleoptile tissue were not related to differences in the final coleoptile length under submergence. In order to find new chromosomal regions associated with the different ability of rice to elongate the coleoptile under submergence, we used genome-wide association study analysis on a panel of 273 japonica rice accessions. We discovered 11 significant marker-trait associations and identified candidate genes potentially involved in coleoptile length. Candidate gene expression analyses indicated that japonica rice genotypes possess complex genetic elements that control final coleoptile length under low oxygen.