A Putative Role for the Tomato Genes DUMPY and CURL-3 in Brassinosteroid Biosynthesis and Response

Abstract

Thedumpy (dpy) mutant of tomato (Lycopersicon esculentum Mill.) exhibits short stature, reduced axillary branching, and altered leaf morphology. Application of brassinolide and castasterone rescued the dpyphenotype, as did C-23-hydroxylated, 6-deoxo intermediates of brassinolide biosynthesis. The brassinolide precursors campesterol, campestanol, and 6-deoxocathasterone failed to rescue, suggesting thatdpy may be affected in the conversion of 6-deoxocathasterone to 6-deoxoteasterone, similar to the Arabidopsisconstitutive photomorphogenesis and dwarfism(cpd) mutant. Measurements of endogenous brassinosteroid levels by gas chromatography-mass spectrometry were consistent with this hypothesis. To examine brassinosteroid-regulated gene expression in dpy, we performed cDNA subtractive hybridization and isolated a novel xyloglucan endotransglycosylase that is regulated by brassinosteroid treatment. The curl-3(cu-3) mutant (Lycopersicon pimpinellifolium [Jusl.] Mill.) shows extreme dwarfism, altered leaf morphology, de-etiolation, and reduced fertility, all strikingly similar to the Arabidopsis mutantbrassinosteroid insensitive 1 (bri1). Primary root elongation of wild-type L. pimpinellifoliumseedlings was strongly inhibited by brassinosteroid application, whilecu-3 mutant roots were able to elongate at the same brassinosteroid concentration. Moreover, cu-3 mutants retained sensitivity to indole-3-acetic acid, cytokinins, gibberellin, and abscisic acid while showing hypersensitivity to 2,4-dichlorophenoxyacetic acid in the root elongation assay. Thecu-3 root response to hormones, coupled with itsbri1-like phenotype, suggests that cu-3may also be brassinosteroid insensitive.