Disruption of <i>DELLA </i>or <i>ERECTA </i>suppresses the enlarged phloem phenotype caused by <i>hawaiian skirt </i>in the tomato cv. Micro-Tom

Modulation of plant vascular tissues is of interest for crop improvement because xylem and phloem are responsible for wood production and sugar transport across the plant, respectively. Previous studies have shown that DELLA and ERECTA (ER) regulate vascular tissue development, as their respective mutants exhibit enlarged xylem and disorganized vascular tissue. The tomato hawaiian skirt-1 (hws-1) mutant accumulates microRNAs and displays a strongly enlarged phloem together with slightly delayed xylem development in pedicels. In this study, della and er mutant lines were crossed with hws-1 to evaluate the effect of disrupted DELLA and ER function on the large-phloem phenotype of hws in the resulting double mutants. Measurement of miRNA164 levels, a microRNA that accumulates in hws, revealed that its abundance returned to wild-type levels in the double mutants, indicating that the effects of della and er mutations dominate over hws. Consistently, plant architecture and vascular phenotypes in the double mutants closely resembled those of the della and er single mutants, and the characteristic phloem enlargement of hws was absent. These results indicate that DELLA and ER functions are required for the manifestation of the hws large-phloem phenotype in tomato cv. Micro-Tom and that these genes are largely epistatic to hws for the majority of the morphological traits examined.