PnOPR6 from Antarctic moss mediates JA-ABA crosstalk and enhances abiotic stress tolerance in Arabidopsis.

Jasmonates (JAs) and abscisic acid (ABA) are vital plant hormones that are integral to the plant's response mechanisms against various abiotic stresses. These hormones also function in an antagonistic manner to regulate seed germination and dormancy. However, little is known about the molecular mechanism underlying the interaction between ABA and JA signaling. Here, seven 12-oxo-phytodienoic acid reductase genes (PnOPR1-7), a key enzyme in the JA biosynthesis pathway, were identified in the Antarctic moss Pohlia nutans transcriptome, and their expressions in response to abiotic stress were examined. Among these, PnOPR6 expression levels rose most under cold and UV-B stresses. Transgenic Arabidopsis overexpressing PnOPR6 demonstrated increased tolerance to salt, cold, dehydration, glucose, and ABA, but also greater sensitivity to methyl jasmonate (MeJA) during seed germination or early root growth. Furthermore, in the transgenic Arabidopsis, PnOPR6 suppressed the expression of genes involved in the ABA pathway and ABI3/5-responsive JA receptor COI1. Additionally, phytohormone metabolomics investigations revealed a significant rise in JA precursor (OPDA, OPC-6, and OPC-4), JA, and its derivative 12-OH-JA in PnOPR6-overexpressing line. Moreover, the accumulation of flavonoid in Arabidopsis was enhanced by heterologous expression of PnOPR6. These findings imply that PnOPR6 functions as a signaling regulator, improving plant resistance to abiotic stress through flavonoid accumulation and JA-ABA antagonistic crosstalk, therefore aiding P. nutans in adjusting to polar climates.