Expression induction of a class of RD26 genes by drought and salinity stresses in maize

RD26 has ability of drought tolerance in dicotyledonous plants, but it is unknown if there are homologs of RD26s in monocotyledonous plants, and if they have ability of drought responses. Here we identified nine homologs of RD26s in maize, each harboring a conserved domain as signature of NAC-family genes. Phylogenetic analyses resulted in three distinct classes, namely Classes I, II and III, respectively. The maize RD26 genes show high divergence in expression, with Zm00001d043094_T001 and Zm00001d034601_T001 dominating expression among Class II genes, and Zm00001d042609_T001 highly were expressed in normal conditions among Class III genes. Three genes in Class II showed significant induction by BR, PEG and NaCl, among which Zm00001d012527_T001 was the most evident with 6.77-fold increase of expression 3 h after induction by PEG. The divergent expression under stresses in different classes of phylogeny suggests functional divergence of the RD26 genes in maize, with genes in Class II only likely be involved in positive response to abiotic stresses, and function as potential targets for future manipulation of maize capability to overcome adverse conditions of drought and salinity.