Root Physiological Traits and Transcriptome Analyses Reveal That Root Zone Water Retention Confers Drought Tolerance to Opisthopappus Taihangensis.

Opisthopappus taihangensis (Ling) Shih, as a relative of chrysanthemum, mainly survives on the cracks of steep slopes and cliffs. Due to the harsh environment in which O. taihangensis lives, it has evolved strong adaptive traits to drought stress. The root system first perceives soil water deficiency, triggering a multi-pronged response mechanism to maintain water potential; however, the drought tolerance mechanism of O. taihangensis roots remains unclear. Therefore, roots were selected as materials to explore the physiological and molecular responsive mechanisms. We found that the roots had a stronger water retention capacity than the leaves. This result was attributed to ABA accumulation, which promoted an increased accumulation of proline and trehalose to maintain cell osmotic pressure, activated SOD and POD to scavenge ROS to protect root cell membrane structure and induced suberin depositions to minimize water backflow to dry soil. Transcriptome sequencing analyses further confirmed that O. taihangensis strongly activated genes involved in the ABA signalling pathway, osmolyte metabolism, antioxidant enzyme activity and biosynthesis of suberin monomer. Overall, these results not only will provide new insights into the drought response mechanisms of O. taihangensis but also will be helpful for future drought breeding programmes of chrysanthemum.