Differential Expression of Genes in the Gibberellin Biosynthetic Pathway Involved in Adaptation to Water Stress in Wild Emmer Wheat Triticum dicoccoides

Drought tolerance mechanisms play an important role in plant adaptation to arid environments. Our previous comparative transcriptome analysis in wild emmer wheat revealed that differential expression of genes involved in metabolism and signaling of absicic acid (ABA), auxin (IAA) and gibberellin (GA), is associated with drought resistance. However, while ABA and IAA related genes had a similar expression patterns in leaves and roots, some of the GA related genes showed opposite trends of expression in the two tissues. The response to drought of additional genes in the GA biosynthetic pathway that were recently published in wheat, and therefore were not represented in the Affymetrix Wheat Array, confirmed the opposite expression patterns in leaves and roots. Furthermore, differential expression between drought resistant and drought susceptible genotypes was found in some of the genes. BLAST analyses of GA genes against sequences from the IWGSC (International Wheat Genome Sequencing Consortium) Survey Sequence revealed that their promoter regions are enriched with transcription factor binding sites related to abiotic stress (e.g. DREB/CBF/ERD/COR) and/or to GA (e.g. GAMYB/GAREAT/CAREOSREP1). GA is an essential hormone involved in many aspects of plant development, but it is not considered as an important stress hormone. Our results indicate that GA is playing an important role in drought response and corroborate with recent publications showing that the cross-talk of GA with ABA and IAA contributes to developmental plasticity under water stress. These processes may lead to increased root biomass and depth, thereby extending the water-absorbing surface area of the roots under drought.