The different root apex zones contribute to drought priming induced tolerance to a reoccurring drought stress in wheat

Drought priming is a promising approach to improve tolerance to further drought in wheat. The root apex plays important roles in drought however, its contribution to drought priming remains unknown. To provide mechanistic insights into this process, the transcriptomes and proteomes at three different zones along the root axis under drought stress were analyzed. Physiological assessment of root growth indicated that priming augmented roots growth in response to drought and also the levels of protective proline and glycine betaine. Scanning across the proximal to the distal zones of the root apex indicated increases the transcription of genes involved in primary and secondary metabolism. Conversely, genes related to translation, transcription, folding, sorting and degradation, replication and repair were increased in the apex compared to the proximal zone. A single drought episode suppressed their expression but prior drought priming served to maintain expression with recurrent drought stress. The differentially primed responses genes were mainly involved in the pathways related to plant hormone signaling, stress defense and cell wall modification. The prediction of regulatory hubs using Cytoscape implicated signaling components such as the ABA receptor PYL4 as influencing antioxidant status and the cell cycle. Based our integrative transcriptomic-proteomic assessments we present a model for drought priming protected plant hormone signaling transduction pathways to drive the cell cycle and cell wall loosening to confer beneficial effects on roots to counter the effects of drought. This model provides a theoretical basis for improvement of drought tolerance in wheat, via an increased understanding of drought priming induced drought tolerance.