A Potential Role for MYB93 Regulating Sulfur Responses in <i>Arabidopsis</i> 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. At MYB93 has a non‐redundant function in lateral root development and redundant functions regulating suberin biosynthesis alongside related MYB transcription factors. Whether At MYB93'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 ( Sl MYB93) 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 At MYB93 in responses to S, while elemental analysis demonstrates that the Atmyb93 mutant has elevated shoot S levels while tomato Sl MYB93‐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.