Thiamine functions as a key activator for modulating plant health and broad‐spectrum tolerance in cotton.

SUMMARY: Global climate changes cause an increase of abiotic and biotic stresses that tremendously threaten the world's crop security. However, studies on broad‐spectrum response pathways involved in biotic and abiotic stresses are relatively rare. Here, by comparing the time‐dependent transcriptional changes and co‐expression analysis of cotton (Gossypium hirsutum) root tissues under abiotic and biotic stress conditions, we discovered the common stress‐responsive genes and stress metabolism pathways under different stresses, which included the circadian rhythm, thiamine and galactose metabolism, carotenoid, phenylpropanoid, flavonoid, and zeatin biosynthesis, and the mitogen‐activated protein kinase signaling pathway. We found that thiamine metabolism was an important intersection between abiotic and biotic stresses; the key thiamine synthesis genes, GhTHIC and GhTHI1, were highly induced at the early stage of stresses. We confirmed that thiamine was crucial and necessary for cotton growth and development, and its deficiency could be recovered by exogenous thiamine supplement. Furthermore, we revealed that exogenous thiamine enhanced stress tolerance in cotton via increasing calcium signal transduction and activating downstream stress‐responsive genes. Overall, our studies demonstrated that thiamine played a crucial role in the tradeoff between plant health and stress resistance. The thiamine deficiency caused by stresses could transiently induce upregulation of thiamine biosynthetic genes in vivo, while it could be totally salvaged by exogenous thiamine application, which could significantly improve cotton broad‐spectrum stress tolerance and enhance plant growth and development. Significance Statement: Thiamine plays a crucial role in regulating plant health and stress resistance. In cotton (Gossypium hirsutum), exogenous thiamine could maintain normal functioning of plants and improve broad‐spectrum stress tolerance by modulating thiamine metabolism and activating calcium signal transduction and stress response pathways. This study has practical significance in enhancing broad‐spectrum stress tolerance of crop plants in changing environments. [ABSTRACT FROM AUTHOR]