Abstract
Mango (Mangifera indica L.) is an important commercial fruit that shows a noticeable loss of firmness during ripening. Polygalacturonase (PG, E.C. 3.2.1.15) is a crucial enzyme for cell wall loosening during fruit ripening since it solubilizes pectin and its activity correlates with fruit softening. Mango PGs were mapped to a genome draft using seventeen PGs found in mango transcriptomes and 48 bonafide PGs were identified. The phylogenetic analysis suggests that they are related to Citrus sinensis, which may indicate a recent evolutive divergence and related functions with orthologs in the tree. Gene expression analysis for nine PGs showed differential expression for them during post-harvest fruit ripening, MiPG21-1, MiPG14, MiPG69-1, MiPG17, MiPG49, MiPG23-3, MiPG22-7, and MiPG16 were highly up-regulated. PG enzymatic activity also increased during maturation and these results correlate with the loss of firmness observed in mango during post-harvest ripening, between the ethylene production burst and the climacteric peak. The analysis of PGs promoter regions identified regulatory sequences associated to ripening such as MADS-box, ethylene regulation like ethylene insensitive 3 (EIN3) factors, APETALA2-like and ethylene response element factors. During mango fruit ripening the action of at least these nine PGs contribute to softening, and their expression is regulated at the transcriptional level. The prediction of the tridimensional structure of some PGs showed a conserved parallel beta-helical fold related to polysaccharide hydrolysis and a modular architecture, where exons correspond to structural elements. Further biotechnological approaches could target specific softening-related PGs to extend mango post-harvest shelf life.
Highlights
Fruit ripening is a physiological, biochemical, and genetically programmed process
Genetic modifications like suppression or over-expression of genes that encode for these hydrolytic enzymes have provided information about their function as well as the redundancy in the function of several isoforms that participate during fruit ripening (Goulao and Oliveira, 2008)
CO2 and ethylene production were measured by gas chromatography (Varian Star 3400, Varian United States) equipped with thermal conductivity (TCD) and flame ionization detectors (FID) and a 2 m × 1/82 metal column filled with Hayesep N 800/100
Summary
Fruit ripening is a physiological, biochemical, and genetically programmed process. This process is characterized by rheological and texture changes as the cell wall is disassembled by the action of hydrolytic enzymes (Li et al, 2010). Mango mesocarp transcriptomes have been obtained (Dautt-Castro et al, 2015, 2018); family members encoding these hydrolases can be identified and further gene expression studies performed to understand more about their roles in the quick softening of mango fruit.
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