Green-fruited Solanum habrochaites lacks fruit-specific carotenogenesis due to metabolic and structural blocks
First author:Himabindu Vasuki Kilambi; Affiliations: University of Hyderabad(海得拉巴大学): Hyderabad, India
Corresponding author:Yellamaraju Sreelakshmi
Members of the tomato clade exhibit a wide diversity in fruit color, but the mechanisms governing inter-species (种间) diversity of coloration (着色) are largely unknown. The carotenoid profiles (类胡萝卜素谱), carotenogenic gene expression and proteome profiles (蛋白谱) of green-fruited Solanum habrochaites (SH; 多毛番茄), orange-fruited S. galapagense (多腺番茄), and red-fruited S. pimpinellifolium (醋栗番茄) were compared with cultivated tomato [S. lycopersicum cv. Ailsa Craig (SL)] to decipher (破译) the molecular basis of coloration diversity. Green-fruited SH, though it showed normal expression of chromoplast-specific (质体特异性) phytoene synthase1 (八氢番茄红素合酶) and lycopene β-cyclase (番茄红素β-环化酶) genes akin to (类似于) orange/red-fruited species, failed to accumulate lycopene and β-carotene (β-胡萝卜素). The SH phytoene synthase1 cDNA encoded an enzymatically active protein, whereas the lycopene β-cyclase cDNA was barely (几乎不) active. Consistent with its green-fruited nature, SH’s fruits retained chloroplast structure and PSII activity, and had impaired (出毛病的) chlorophyll degradation with high pheophorbide a (脱镁叶绿酸a) levels. Comparison of the fruit proteomes with SL revealed retention of the proteome complement related to photosynthesis in SH. Targeted peptide monitoring (靶向肽追踪) revealed a low abundance of key carotenogenic and sequestration proteins (封存) in SH compared with tomato. The green-fruitedness of SH appears to stem from (由…造成) blocks at several critical steps regulating fruit-specific carotenogenesis namely the absence of chloroplast to chromoplast transformation, block in carotenoid biosynthesis, and a dearth (缺乏) of carotenoid sequestering proteins.