GENE EXPRESSION PROFILING OF TOMATO FRUIT RIPENING

Department of Horticulture Texas A&M University College Station, Texas 77843

The ripening of fleshy fruits is a complex developmental process influenced by numerous factors including light, hormones, temperature, and genotype. Tomato has long served as a model organism for climacteric ripening, resulting in the development of numerous genetic and molecular tools for analysis including a substantial EST database and well characterized transgenic and genetic variants influencing various aspects of fruit maturation. The recent advent of cDNA microarray technology provides us the opportunity to monitor genome-wide expression during fruit ripening. Our objective is to develop expression profiles that will elucidate the underlying molecular events and genetic regulation involved in the ripening phenomenon. Initially, we have chosen 679 non-redundant ESTs sequenced from an early ripening fruit ("breaker"; 35-37 dpa) cDNA library for expression analysis in four specific developmental stages: mature green, mature green treated with ethylene, breaker, and red ripe. Fluorescent-labeled cDNA probes were prepared utilizing mRNA isolated from the aforementioned tissues and subsequently applied to the breaker microarrays. Hybridization intensities were quantified and correlated with RNA-blot analysis to normalize expression profiles. This information, coupled with corresponding physiological variation among developmental stages analyzed, will eventually provide specific targets for genetic manipulation of fruit development and associated quality and nutritional characteristics. Ultimately, the optimization of this technology should facilitate a comparative analysis of genome-wide transcript accumulation during fruit development and as influenced by relevant regulatory gene mutations and hormonal and environmental stimuli. We will describe our current efforts on standardizing microarray analysis within our laboratory and present preliminary data on fruit ripening expression profiles.