Genome-Wide Identification of Mango (Mangifera indica L.) Polygalacturonases: Expression Analysis of Family Members and Total Enzyme Activity During Fruit Ripening

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.

Genome-wide analysis of polygalacturonase gene family from pear genome and identification of the member involved in pear softening

“…Cell wall is consisted of complex polysaccharides, including pectin, cellulose, and hemicellulose [3]. A variety of enzymes, including PG, pectinesterase (PE), β-galactosidase (β-Gal), cellulase and xyloglucan endo-transglycosylase (XET), are proposedly involved in the metabolism of these components [7, 24].…”

“…Pectin is a structural polysaccharide of the primary cell wall and middle lamella, playing an important role in cell-to-cell adhesion [7]. PG is the key enzyme involved in its degradation, through cleavage of α-(1 → 4) glycoside bonds [7, 25]. Until recently, PG family genes have been characterized from many plants [6, 8, 9, 26].…”

“…Until recently, PG family genes have been characterized from many plants [6, 8, 9, 26]. Besides fruit softening, PG also functions in many developmental processes of plant, such as flower development or abscission zone development [7]. During ‘Huanghua’ pear storage, firmness demonstrated an opposite trend when compared with that of PG activity [19].…”

“…Belonging to one of the largest hydrolase families, polygalacturonase (PG), which was discovered half a century ago, has known to be involved in various processes of plant development, such as flower development, fruit ripening & senescence and organ abscission [5–7]. PG plays an important role in pectin disassembly, and could be divided into three types based on different catalytic processes, including endo-PGs, exo-PGs, and rhamno-PGs [6].…”

“…Eleven members from Populus were proposed to be involved in flower development, while two related to leaf abscission under salt stress [9]. Of 54 SlPGs identified from tomato fruit, members in clade A and B were involved in fruit and abscission zone development, while members from clade C, D, and F in flowering development [7]. Three PpPGs supposedly participated in the softening process of peach [8].…”