Physiological and RNA-Seq Analyses on Exogenous Strigolactones Alleviating Drought by Improving Antioxidation and Photosynthesis in Wheat (<i>Triticum aestivum</i> L.)

Drought poses a significant challenge to global wheat production, and the application of exogenous phytohormones offers a convenient approach to enhancing drought tolerance of wheat. However, little is known about the molecular mechanism by which strigolactones (SLs), newly discovered phytohormones, alleviate drought stress in wheat. Therefore, this study is aimed at elucidating the physiological and molecular mechanisms operating in wheat and gaining insights into the specific role of SLs in ameliorating responses to the stress. The results showed that SLs application upregulated the expression of genes associated with the antioxidant defense system (<i>Fe/Mn-SOD</i>, <i>PER1</i>, <i>PER22</i>, <i>SPC4</i>, <i>CAT2</i>, <i>APX1</i>, <i>APX7</i>, <i>GSTU6</i>, <i>GST4</i>, <i>GOR</i>, <i>GRXC1</i>, and <i>GRXC15</i>), chlorophyll biogenesis (<i>CHLH</i>, and <i>CPX</i>), light-harvesting chlorophyll A-B binding proteins (<i>WHAB1.6</i>, and <i>LHC Ib-21</i>), electron transfer (<i>PNSL2</i>), E3 ubiquitin-protein ligase (<i>BB</i>, <i>CHIP</i>, and <i>RHY1A</i>), heat stress transcription factor (<i>HSFA1</i>, <i>HSFA4D</i>, and <i>HSFC2B</i>), heat shock proteins (<i>HSP23.2</i>, <i>HSP16.9A</i>, <i>HSP17.9A</i>, <i>HSP21</i>, <i>HSP70</i>, <i>HSP70-16</i>, <i>HSP70-17</i>, <i>HSP70-8</i>, <i>HSP90-5</i>, and <i>HSP90-6</i>), DnaJ family members (<i>ATJ1</i>, <i>ATJ3</i>, and <i>DJA6</i>), as well as other chaperones (<i>BAG1</i>, <i>CIP73</i>, <i>CIPB1</i>, and <i>CPN60I</i>). but the expression level of genes involved in chlorophyll degradation (<i>SGR</i>, <i>NOL</i>, <i>PPH</i>, <i>PAO</i>, <i>TIC55</i>, and <i>PTC52</i>) as well as photorespiration (<i>AGT2</i>) was found to be downregulated by SLs priming. As a result, the activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) were enhanced, and chlorophyll content and photosynthetic rate were increased, which indicated the alleviation of drought stress in wheat. These findings demonstrated that SLs alleviate drought stress by promoting photosynthesis through enhancing chlorophyll levels, and by facilitating ROS scavenging through modulation of the antioxidant system. The study advances understandings of the molecular mechanism underlying SLs-mediated drought alleviation and provides valuable insights for implementing sustainable farming practice under water restriction.