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Plant Physiology Preview Published on May 8, 2008; 10.1104/pp.108.119917
Received March 27, 2008 An evaluation of the basis and consequences of a stay-green mutation in the navel negra (nan) citrus mutant using transcriptomic and proteomic profiling and metabolite analysis
Instituto Valenciano de Investigaciones Agrarias. Centro de Genomica. Ctra. Moncada-Naquera Km 5, 46113 Moncada, Valencia, Spain; Chemistry and Biochemistry Pigments Group, Food Biotechnology Department, Instituto de la Grasa, Consejo Superior de Investigaciones Cientificas (CSIC), Sevilla, Spain; Department of Plant Biology, Cornell University, Ithaca, NY 147853, USA; USDA Plant Soils and Nutrition Laboratory, Tower Road, Cornell University, Ithaca, NY 14853 USA * Corresponding author; email: mtalon{at}ivia.es.
A Citrus sinensis spontaneous mutant, navel negra (nan), produces fruit with an abnormal brown colored flavedo during ripening. Analysis of pigment composition in the wild type (WT) and nan flavedo suggested that typical ripening-related chlorophyll (Chl) degradation, but not carotenoid biosynthesis, was impaired in the mutant, identifying nan as a Type C stay-green mutant. nan exhibited normal expression of Chl biosynthetic and catabolic genes and chlorophyllase activity, but no accumulation of dephytylated chlorophyll compounds during ripening, suggesting that the mutation is not related to a lesion in any of the principal enzymatic steps in Chl catabolism. Transcript profiling using a citrus microarray indicated that a citrus ortholog of a number of SGR (stay green) genes was expressed at substantially lower levels in nan, both prior to, and during, ripening. However, the pattern of catabolite accumulation and SGR sequence analysis suggested that the nan mutation is distinct from those in previously described stay-green mutants and is associated with an upstream regulatory step, rather than directly influencing a specific component of Chl catabolism. Transcriptomic and comparative proteomic profiling further indicated that the nan mutation resulted in the suppressed expression of numerous photosynthesis-related genes and in the induction of genes that are associated with oxidative stress. These data, in addition to metabolite analyses, suggest that nan fruit employ a number of molecular mechanisms to compensate for the elevated Chl levels and associated photooxidative stress.
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