Gene expression analysis of in vitro cultured tomato plantlets

Plants growth and development is highly dependent on the environment. During there lifespan, plants are submitted to changing environmental conditions that requires constant metabolic adjustments. In particular, in vitro cultured plantlets are exposed, throughout micropropagation, to unique growth conditions characterized by distinctive levels of nitrogen, exogenous sugar, light and atmospheric conditions. To resume growth upon transfer ex vitro, in vitro plantlets must acclimatize to natural conditions. In this study, the impact of the in vitro environment on the expression profile of tomato (Solanum Lycopersicum) plantlets was analysed using the microarray and real-time PCR methods. After 20 days of growth in vitro, a significant increase in expression of genes linked to photosynthesis, nitrogen metabolism and salicylic acid signaling pathways was observed. By opposition, the expression of transcripts associated to carbohydrate metabolism and jasmonic acid signaling pathway were reduced. Also, the expression of reactive oxygen scavenging (ROS) enzymes in the mitochondrias, chloroplasts and cytosol were altered in in vitro cultured tomato plantlets. More precisely, the in vitro environment led to increased photosynthetic gene expression, lower sink strength, up-regulation of nitrogen assimilation and induced a specific stress response in tomato plantlets. Our results suggest that the presence of exogenous sugar is an important environmental cue that governs the modified cell ROS pattern, defense-related genes modulation and abnormal physiology of in vitro plantlets. Keywords: environmental challenge, growth condition comparison, expression profile Three biological replicates consisting of three individual plantlets grown in different vessels (in vitro) or pots (ex vitro) were used for the competitive hybridization. To reduce possible bias due to the difference in the properties of both dyes, two technical replicates consisting of dye swap were realized. The complete experiment required six microarrays.