Rapid formation of adventitious roots and partial ethylene sensitivityresult in faster adaptation to flooding in the aerial roots (aer) mutantof tomato

Abstract

The frequency of extreme events such as droughts and floods has increased as a consequence of climatechange. Many crops have not been improved to tolerate soil anoxia and, therefore, floods cause importanteconomic losses. During submergence, Solanum lycopersicum L. exhibits three distinct responses whichare adventitious root production, epinasty and aerenchyma formation. The development of a new adven-titious root system is crucial as it can replace the original roots that succumb to the hypoxic environment.Aerial roots (aer) is a tomato mutant characterized by the presence of numerous adventitious root pri-mordia along the hypocotyl and older internodes. In this work, we have analyzed the aer mutant behaviorto flooding to determine whether preformed adventitious roots represent an adaptive advantage withrespect to biomass accumulation. We have also examined other morphological and anatomical responsesof aer plants to detect differential adaptations under flooding. Aer plants form an abundant adventitiousroot system faster than Ailsa Craig cultivar, which results in flooded plants accumulating as much biomassas non-flooded aer plants. In addition, several ethylene-induced responses such as epinasty, hypertrophy,aerenchyma production, and apical hook formation are reduced in aer, suggesting a lower sensitivity ofsome tissues to ethylene. The E4 expression level, an ethylene-induced gene, confirmed this observationsince E4 transcripts are less abundant in petioles and stems of ethylene-treated aer plants, coinciding withthe tissues that present a lower degree of morphological and/or anatomical response. Evidence from theNever ripe mutant suggests a reduction in ethylene sensitivity could contribute to the attenuation offlooding effects. Therefore, our results indicate that the rapid formation of a new root system togetherwith a reduction in ethylene sensitivity is responsible of a faster adaptation to flooding stress in the aermutant.