Growth responses of seedlings under complete submergence in rice cultivars carrying both the submergence-tolerance gene <i>SUB1A-1</i> and the floating genes <i>SNORKEL</i>s

We screened 80 Asian rice (<i>Oryza sativa</i> L.) cultivars for the presence of the submergence-tolerance gene <i>SUB1A-1</i> and the floating genes <i>SNORKEL1</i> (<i>SK1</i>) and <i>SNORKEL2</i> (<i>SK2</i>), and found that the deepwater rice cultivar Baisbish (BSB) and the submergence-tolerant cultivar Flood Resistant 13A (FR13A) both possess the <i>SUB1A-1</i> and the <i>SK1</i>/<i>2</i>. When BSB and FR13A seedlings were completely submerged, spindly growth of shoots was induced in BSB but not in FR13A. Submergence significantly increased the <i>SUB1A-1</i> transcript abundance in BSB and FR13A shoots, but the expression level in BSB was much lower than that of FR13A. Submergence also induced the expression of both <i>ERF66</i> and <i>ERF67</i>, the transcriptional targets of SUB1A-1, in FR13A shoots, whereas it upregulated the expression of <i>ERF67</i> but not that of <i>ERF66</i> in BSB shoots. These results suggest that BSB could not display submergence tolerance due to the low expression of <i>SUB1A-1</i> and/or <i>ERF66</i> under submergence.