Flavonoid and isoflavonoid biosynthetic gene expression is affected by MYB36 transcription factor deficiency in Lotus...

MYB36 was recently identified as a transcription factor (TF) that may be involved in isoflavonoid metabolism and stress responses in the model legume Lotus japonicus. To further explore its role, we performed a comparative transcriptomic and (iso)flavonoid profiling analysis of wild-type (WT) plants and two independents homozygous Ljmyb36 mutant lines under two abiotic stress conditions: UV-B irradiation and salinity. The results obtained showed a markedly distinct and almost reciprocal global transcriptomic response of WT plants under both types of stress conditions. Under UV-B irradiation, genes related to isoflavonoid biosynthesis were induced, accompanied by increased isoflavonoid accumulation. In contrast, under salt stress, most of the genes modulated in the mutants corresponded to genes specifically involved in isoflavonoid, but not flavonol biosynthesis, highlighting candidate genes potentially regulated by MYB36. Metabolite profiling also indicated opposite changes in flavonoid and isoflavonoid metabolite in response to salt and UV-B treatments, reflecting the reciprocal patterns of gene expression found in salt and UV-B treatment conditions. These results suggest a role, for the first time, of MYB36 as a specific transcription factor in the regulation of (iso)flavonoid biosynthesis. In addition, the results obtained support the role of MYB36 as a crucial TF in the response to salt stress in legume plants.