A Potential Role for MYB93 Regulating Sulfur Responses in Arabidopsis and Tomato

ABSTRACT Sulfur (S) is an important nutrient that has wide‐ranging effects on plant health and metabolism. Several classes of transcription factors respond to S deprivation, including R2R3‐MYBs. In Arabidopsis, the AtMYB93 transcription factor‐encoding gene is upregulated by S deprivation. AtMYB93 has a non‐redundant function in lateral root development and redundant functions regulating suberin biosynthesis alongside related MYB transcription factors. Whether AtMYB93's potential role in plant S responses relates to lateral root development, and the extent to which either function is conserved outside Arabidopsis, are unknown. We show that a tomato MYB93 homolog (SlMYB93) can inhibit lateral root development in Arabidopsis. Putative MYB93 homologs in many dicots show root enrichment and tomato MYB93‐related genes show upregulation by S stress. The transcriptome of Atmyb93 mutant roots implicates AtMYB93 in responses to S, while elemental analysis demonstrates that the Atmyb93 mutant has elevated shoot S levels while tomato SlMYB93‐overexpressing plants have reduced shoot S. We uncover a stimulatory effect of S deprivation on Arabidopsis adventitious root development. However, Atmyb93 mutants do not show significant changes in sensitivity to S with respect to lateral or adventitious root development, most likely due to some functional redundancy. Moreover, AtMYB93 promoter activity is not spatially regulated by S deprivation. Taken together, our data suggest that MYB93 may have a role in mediating the regulation of S levels alongside other root transcription factors.