Expression of rice SUB1A and SUB1C transcription factors in Arabidopsis uncovers flowering inhibition as a submergence tolerance mechanism.

Submergence of plant organs perturbs homeostasis by limiting diffusion of oxygen, carbon dioxide and ethylene. In rice (Oryza sativa L.), the haplotype at the multigenic SUBMERGENCE1 (SUB1) locus determines whether plants survive prolonged submergence. SUB1 encodes two or three transcription factors of the group VII ethylene response factor family: SUB1A, SUB1B and SUB1C. The presence of SUB1A-1 and its strong submergence-triggered ethylene-mediated induction confers submergence tolerance through a quiescence survival strategy that inhibits gibberellin (GA)-induced carbohydrate consumption and elongation growth. SUB1C is invariably present and acts downstream of the enhancement of GA responsiveness during submergence. In this study, heterologous ectopic expression of rice SUB1A and SUB1C in Arabidopsis thaliana was used to explore conserved mechanisms of action associated with these genes using developmental, physiological and molecular metrics. As in rice transgenic plants that ectopically express SUB1A-1, Arabidopsis transgenic plants that constitutively express SUB1A displayed GA insensitivity and abscisic acid hypersensitivity. Ectopic SUB1C expression had more limited effects on development, stress responses and the transcriptome. Observation of a delayed flowering phenotype in lines over-expressing SUB1A led to the finding that inhibition of floral initiation is a component of the quiescence survival strategy in rice. Together, these analyses demonstrate conserved as well as specific roles for group VII ethylene response factors in integration of abiotic responses with development.