Genetic variation in ZmSO contributes to ABA response and drought tolerance in maize seedlings

Water scarcity impairs maize growth and yield. Identification and deployment of superior drought-tolerance alleles is desirable for the genetic improvement of stress tolerance in maize. Our previous study revealed that maize sulfite oxidase (SO) catalyzes the oxidation of sulfite to sulfate and may be involved in drought response. But it was unclear whether the natural variation in ZmSO is directly associated with the drought resistance of maize. In the present study, we showed that ZmSO was associated with drought tolerance in maize seedlings, using gene association analysis and a transgene approach. A 14-bp insertion variation, containing two ABA-responsive elements, in the promoter region of ZmSO conferred ABA-inducible expression, leading to increased drought tolerance. Genetic selection of this favorable allele increased drought tolerance. This study has identified elite alleles associated with sulfur metabolism for improving maize drought resistance.