Flood adaptive traits and processes: An overview

'Summary' 57 I. 'Introduction' 58 II. 'Root acclimations that promote root aeration' 60 III. 'Regulating reaeration by active emergence in Rumex palustris and Oryza sativa' 62 IV. 'Limiting O2 starvation with gas films and underwater photosynthesis' 64 V. 'Key metabolic acclimations to flooding and low-O2 stress and their control' 65 VI. 'Managing quiescence in growth during submergence' 67 VII. 'After the deluge' 68 VIII. 'Perspective' 69 'Acknowledgements' 69 References 69 Summary Unanticipated flooding challenges plant growth and fitness in natural and agricultural ecosystems. Here we describe mechanisms of developmental plasticity and metabolic modulation that underpin adaptive traits and acclimation responses to waterlogging of root systems and submergence of aerial tissues. This includes insights into processes that enhance ventilation of submerged organs. At the intersection between metabolism and growth, submergence survival strategies have evolved involving an ethylene-driven and gibberellin-enhanced module that regulates growth of submerged organs. Opposing regulation of this pathway is facilitated by a subgroup of ethylene-response transcription factors (ERFs), which include members that require low O2 or low nitric oxide (NO) conditions for their stabilization. These transcription factors control genes encoding enzymes required for anaerobic metabolism as well as proteins that fine-tune their function in transcription and turnover. Other mechanisms that control metabolism and growth at seed, seedling and mature stages under flooding conditions are reviewed, as well as findings demonstrating that true endurance of submergence includes an ability to restore growth following the deluge. Finally, we highlight molecular insights obtained from natural variation of domesticated and wild species that occupy different hydrological niches, emphasizing the value of understanding natural flooding survival strategies in efforts to stabilize crop yields in flood-prone environments.