Differential involvement of MYB13 and MYB15 transcription factors in isoflavonoid biosynthesis and tolerance to salt stress in Lotus japonicus

• Two transcription factors called MYB13 and MYB15 have been studied in relation to abiotic stress. • MYB13 has been identified as a key factor in salt tolerance in L. japonicus . • Modifications in root architecture and differences in vestitol and Cl - contents are described as possible factors involved in Ljmyb13 salt stress acclimation. • MYB15 acts as a positive regulator of isoflavonoid biosynthesis in response to UV-B irradiation in this plant. Understanding the mechanisms involved in the response to abiotic stress is essential to enhance plant stress resilience and ensure sustainable agriculture. In this study we report different roles for two closely related MYB transcription factors (TFs), MYB13 and MYB15, in the legume model Lotus japonicus . Different growth and biochemical parameters were determined for mutant lines impaired in these TFs under either control conditions or under two different types of abiotic stress: salinity and UV-B irradiation. Our findings show that MYB15 positively regulates isoflavonoid biosynthesis under UV-B irradiation but does not affect salt tolerance. In contrast, MYB13 does not appear to be involved in the UV-B response but plays a significant role in salt stress tolerance, as specific mutants lacking MYB13 exhibited increased NaCl resistance. Further analysis revealed that salt tolerance in Ljmyb13 mutants is associated with changes in vestitol and chloride ion (Cl - ) levels, as well as modifications in root architecture. Moreover, the growth of both mutants was enhanced in the absence of abiotic stress, but only under non-symbiotic conditions. These findings highlight the differential roles of MYB13 and MYB15 in regulating stress responses and provide insights into potential mechanisms of salt stress adaptation in L. japonicus .