Location: Plant, Soil and Nutrition ResearchTitle: Altered chloroplast development and delayed fruit ripening caused by mutations in a zinc metalloprotease at the lutescent 2 locus of tomato Author
Submitted to: Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/21/2012
Publication Date: 5/22/2012
Publication URL: http://dx.doi.org/10.1104/pp.112.197483
Citation: Barry, C., Aldridge, G., Herzog, G., Ma, Q., Mcquinn, R., Hirschberg, J., Giovannoni, J.J. 2012. Altered chloroplast development and delayed fruit ripening caused by mutations in a zinc metalloprotease at the lutescent 2 locus of tomato. Plant Physiology. 159:1086-1098. Interpretive Summary: Plant chloroplasts serve as the site of photosynthesis as well as production of important nutrients and a range of specialized metabolites (e.g. antioxidant carotenoids). Fruit ripening is marked by a reprogramming of chloroplast metabolism emphasizing nutrient and quality attributes, transforming the fruit from an unpalatable and often toxic organ into one that is attractive and nutritious. We have identified and characterized the tomato L2 gene which is a genetic link between chloroplast development and the transition to fruit ripening. The greater understanding of fruit development resulting from this work should facilitate crop improvement strategies resulting in more nutritious and attractive fruit.
Technical Abstract: The chloroplast is the site of photosynthesis in higher plants but also functions as the center of synthesis for primary and specialized metabolites including amino acids, fatty acids, starch, and diverse isoprenoids. Mutants that disrupt aspects of chloroplast function represent valuable tools for defining structural and biochemical regulation of the chloroplast and its interplay with whole plant structure and function. The lutescent 1 (l1) and lutescent 2 (l2) mutants of tomato (Solanum lycopersicum) possess a range of chlorophyll deficient phenotypes including reduced rates of chlorophyll synthesis during de-etiolation and enhanced rates of chlorophyll loss in leaves and fruits as they age, particularly in response to high-light stress and darkness. In addition, the onset of fruit ripening is delayed in lutescent mutants by approximately one week although once ripening is initiated they ripen at a normal rate and accumulation of carotenoids is not impaired. The l2 locus was mapped to the long arm of chromosome 10 and positional cloning revealed the existence of a premature stop codon in a chloroplast targeted zinc metalloprotease of the M50 family that is homologous to the Arabidopsis gene ETHYLENE-DEPENDENT GRAVITROPISM DEFICIENT AND YELLOW-GREEN 1 (EGY1). Screening of tomato germplasm identified two additional l2 mutant alleles. This study suggests a role for the chloroplast in mediating the onset of fruit ripening in tomato and indicates that chromoplast development in fruit does not depend on functional chloroplasts.