Integrative Comparative Analyses of Transcript and Metabolite Profiles from Pepper and Tomato Ripening and Development Stages Uncovers Species-Specific Patterns of Network Regulatory Behavior  

Integrative comparative analyses of transcript and metabolite levels from climacteric and nonclimacteric fruits can be employed to unravel the similarities and differences of the underlying regulatory processes. To this end, we conducted combined gas chromatography-mass spectrometry and heterologous microarray hybridization assays in tomato (Solanum lycopersicum; climacteric) and pepper (Capsicum chilense; nonclimacteric) fruits across development and ripening. Computational methods from multivariate and network-based analyses successfully revealed the difference between the covariance structures of the integrated data sets. Moreover, our results suggest that both fruits have similar ethylene-mediated signaling components; however, their regulation is different and may reflect altered ethylene sensitivity or regulators other than ethylene in pepper. Genes involved in ethylene biosynthesis were not induced in pepper fruits. Nevertheless, genes downstream of ethylene perception such as cell wall metabolism genes, carotenoid biosynthesis genes, and the never-ripe receptor were clearly induced in pepper as in tomato fruit. While signaling sensitivity or actual signals may differ between climacteric and nonclimacteric fruit, the evidence described here suggests that activation of a common set of ripening genes influences metabolic traits. Also, a coordinate regulation of transcripts and the accumulation of key organic acids, including malate, citrate, dehydroascorbate, and threonate, in pepper fruit were observed. Therefore, the integrated analysis allows us to uncover additional information for the comprehensive understanding of biological events relevant to metabolic regulation during climacteric and nonclimacteric fruit development.