Transcriptome analysis reveals potential mechanisms for inhibition of intumescence development by UV radiation in tomato

Intumescence is a physiological disorder characterized by epidermal cell hypertrophy in many plant species, including tomato. Although previous studies have been focused on identifying the environmental conditions associated with intumescence development, fundamental molecular responses of plants during the development of the disorder are unknown. Our recent work demonstrates that intumescences can be induced by blocking plant exposure to ultraviolet (UV) radiation. To understand how UV influences intumescence development at the molecular level, we grew an intumescence-sensitive tomato cultivar, Maxifort, under environmental conditions either with UV or blocked-UV. Extensive intumescences were induced in leaves grown under the blocked-UV condition, and a comparison of the gene expression profiles of leaf tissues with and without intumescences indicated that there were 1604 genes differentially expressed. The genes were involved in several important cellular processing groups, including hormone response, DNA synthesis and repair, metabolic pathways and cell wall biosynthesis. Furthermore, most of the photosynthesis-associated genes were uniformly repressed in the leaves with intumescences. Ethylene biosynthesis and its downstream signal transduction pathway were particularly more active in leaves with intumescences than in those without intumescences, suggesting that ethylene signaling may play a role in occurrence of intumescence. We further analyzed the interaction between UV treatment and intumescence-related genes to determine how UV inhibits the development of intumescences and identified a number of genes that could be induced by UV treatment but suppressed in the leaves with intumescences. Among them, an important gene, 3-beta hydroxysteroid dehydrogenase (3β − HSD), might play a key role in UV inhibition of intumescence development. Taken together, the results of this study provide insights into the mechanisms regulating the development of intumescences at the molecular level in tomato.