Responses of the Australian Wild Rice Oryza meridionalis to Complete Submergence

We investigated the presence or absence of the SUB1A gene, which confers submergence tolerance in Oryza sativa L., in seven accessions of Australian wild rice ( Oryza meridionalis Ng.) and detected SUB1A in four accessions. O. meridionalis SUB1A ( OmeSUB1A ), which exhibits 78.6%–78.8% identity with O. sativa SUB1A ( OsSUB1A ), was branched into a separate clade from other SUB1A genes of AA genome rice species through phylogenetic analysis. SUB1A -positive O. meridionalis accessions displayed no significant shoot elongation induced by submergence with increased expression of the SUB1A gene. Contrastingly, submergence significantly induced shoot elongation in SUB1A -negative accessions. The expression level of the SUB1A in submerged O. meridionalis accessions possessing SUB1A was positively correlated with the post-submergence survival rate of plants. Moreover, in SUB1A -positive O. meridionalis accessions, submergence significantly upregulated the expression of ERF66 and ERF67 , which are transcriptionally targeted by SUB1A for inducing submergence tolerance in O. sativa ; however, these interactions are not detected in SUB1A -negative accessions. These findings suggest that some accessions of O. meridionalis harbor SUB1A and are therefore able to adapt to short-term complete submergence through a quiescent strategy by inhibiting elongation growth, and that the underlying molecular mechanism is the same as that in submergence-tolerant cultivars of O. sativa .