Understanding the Mechanisms Regulating the Development of Intumescences In Tomato Through Genomic Analyses

    Intumescences are physiological disorder characterized by cell hyperplasia that have been observed in tomato and other plant species for over a hundred years.  Extensive intumescence development can result in significant yield losses. Previous research focused on identifying the environmental conditions that result in intumescence development, but fundamental physiological and molecular changes of plants during the development of the disorder remain to be explored. Our previous research has suggested that intumescences can be induced by blocking plant exposure to ultraviolet light in the wavelength range of 280-320 nm (UVB). To investigate the physiological changes of tomato leaves during the development of intumescences and understand how UVB influences intumescence development, we grew the intumescence-sensitive cultivar of tomato, Solanum lycopersicum L. var. hirsutum Humb. & Bonpl. ‘Maxifort’, in either with UVB or blocked UVB environments. Leaves grown under the blocked UVB condition developed extensive intumescences. Leaf tissue was subjected to microarray analysis using Affymetrix tomato GeneChips. A comparison of the gene expression profiles of leaves with and without intumescences indicated that there were 1604 genes that showed differentially regulated patterns. The changed genes were involved in several important cellular process groups, such as hormone response, DNA synthesis and repair, metabolic pathways, and cell wall biosynthesis. Interestingly, almost all the photosynthesis genes covered in this tomato genechip were uniformly repressed in the leaves with intumescences, which suggests that intumescences may reduce yield by decreasing the efficiency of photosynthesis. By conducting biological pathway analysis, we found that ethylene biosynthesis and its downstream signal transduction pathway were more active in leaves with intumescences; this suggests that intumescences may be controlled by regulating ethylene signaling. By investigating the interaction between UVB treatment and intumescence gene regulation networks, we also identified an important gene, 3-beta hydroxysteroid dehydrogenase, that could be induced by UVB treatment but suppressed in leaves with intumescences. This enzyme may be a key in explaining why UVB exposure can abate intumescence development in tomato. The results of this study provide further insights into the mechanisms regulating the development of intumescences in tomato.