GmMYB84, a transcription factor, confers cadmium tolerance in soybean via regulation of the phenylpropanoid pathway

GmMYB84, an R2R3-MYB transcription factor, plays a vital role in regulating plant responses to abiotic stress. To elucidate how GmMYB84 mediates Cd tolerance, we performed functional analyses using overexpression lines (OE-GmMYB84) in Arabidopsis thaliana and CRISPR/Cas9 knockout mutants (myb84) in soybean. The Arabidopsis ortholog, AtMYB116, shows Cd-sensitive phenotypes, suggesting a possible functional link between this MYB module and Cd responses. Accordingly, GmMYB84 overexpression in Arabidopsis plants significantly enhanced Cd tolerance, as evidenced by increased germination rates, root length, leaf dry weight, chlorophyll content, and flavonoid levels, along with decreased oxidative damage markers of hydrogen peroxide (H₂O₂) and malondialdehyde (MDA) compared to wild-type (WT) plants. In contrast, GmMYB84-knockout soybean lines generated by CRISPR/Cas9 exhibited severe growth inhibition, decreased antioxidant capacity, and elevated oxidative stress under Cd exposure. This observation suggest that GmMYB84 is associated with phenylpropanoid-related responses under Cd stress. Glyma.01G172700 (encoding phenylcoumaran benzylic ether reductase, a key enzyme in lignin biosynthesis) and Glyma.02G042500 (encoding class I chitinase, involved in chitinase-mediated defense responses) are therefore considered putative targets in our working model. Our findings support a working model linking GmMYB84 to Cd tolerance and provide a candidate target for breeding or biotechnological strategies to improve Cd resilience in soybean.