Drought Stress Inhibits the Accumulation of Rotenoids and the Biosynthesis of Drought-Responsive Phytohormones in Mirabilis himalaica (Edgew.) Heim Calli

<b>Background:</b><i>Mirabilis himalaica</i>, distributed in the high-altitude, arid, and semi-arid regions of Xizang, exhibits great tolerance to drought, which is rich in rotenoids and other secondary metabolites. It is still unknown, though, how drought stress influences rotenoid synthesis in <i>M. himalaica</i>. <b>Methods</b>: In this study, the calli of <i>M. himalaica</i> were subjected to 5% PEG6000 for 0, 20, and 40 h and divided into control group (CK), mild-drought-treated group (M), and high-drought-treated group (H), respectively. We then analyzed the relative content of three main rotenoids in <i>M. himalaica</i> using high-performance liquid chromatography-electrospray ionization-tandem mass spectrometry (HPLC-ESI-MS/MS). <b>Results</b>: Our findings demonstrated that the content of rotenoids was significantly reduced under drought stress. Transcriptome analysis subsequently revealed 14,525 differentially expressed genes (DEGs) between the different treatments. Furthermore, these DEGs exhibited enrichment in pathways associated with isoflavone biosynthesis and hormone signaling pathways. Key genes with decreased expression patterns during drought stress were also found to be involved in rotenoid accumulation and drought-responsive phytohormone signaling, including abscisic acid (ABA), auxin (IAA), and jasmonic acid (JA). <b>Conclusions</b>: These findings elucidate the molecular processes of drought resistance in <i>M. himalaica</i> and shed light on the relationship between rotenoid production and drought stress in <i>M. himalaica</i>.