Comparative analysis of pectate lyase in relation to softening in strawberry fruits

Abstract

Strawberry fruits are perishable due to fruit softening occurring during storage and marketing, but the mechanism by which this occurs is not clear. In this study, the possible mechanism of softening is explored by comparative studies on the changes of fruit firmness, pectate lyase (PL) activities, and relative expression levels of PL genes between two strawberry cultivars. The results indicate that a method for the determination of PL activity in the strawberry fruit was established. The activity of PL was at a low level in the small green fruit to white fruit stage, and maintained at a high level in the ripening and softening stage. The PL gene was specifically expressed in fruit and mainly in the ripening stage. PL expressions were closely correlated with PL activities, and negatively related with the changes in flesh firmness. The full-length cDNA of PL genes from the two cultivars was cloned using the RACE method. Amino acid residues of C terminal sequences of the PL proteins from different species showed significant variations. Those results suggested that the differences in PL activity, gene sequence, and gene expression patterns may lead to the different roles of PL in different fruit textures of strawberries during ripening and softening.Key words: fruit ripening and softening, pectate lyase, strawberry.Résumé : La fraise est un fruit périssable parce que la baie ramollit pendant l'entreposage et la vente, mais on ne sait pas exactement quel mécanisme est à l'origine de ce phénomène. Les auteurs se sont efforcés de le préciser en comparant les changements qui surviennent au niveau de la fermeté du fruit, de l'activité de la pectate lyase (PL) et de l'expression relative des gènes PL chez deux cultivars de fraisier. Les résultats ont permis d'établir une méthode pour jauger l'activité de la PL chez la fraise. La PL est peu active dans les petites baies vertes, jusqu'au stade du fruit blanc, après quoi elle reste très active pendant le mûrissement et le ramollissement. Le gène PL s'exprime spécifiquement chez le fruit et surtout pendant le mûrissement. L'expression du gène PL est étroitement corrélée à l'activité de la PL et négativement reliée aux changements de fermeté de la chair. Les auteurs ont cloné l'ADNc complet des gènes PL des deux cultivars par la technique RACE. Les résidus des acides aminés de la séquence C finale des protéines PL varient significativement entre les deux variétés. Ces résultats donnent à penser que les écarts au niveau de l'activité de la PL, de la séquence génétique et de l'expression des gènes pourraient expliquer le rôle variable de la PL dans les diverses textures observées chez la fraise pendant le mûrissement et le ramollissement. [Traduit par la Rédaction] Mots-clés : fraise, pectate lyase, mûrissement, ramollissement du fruit.

PpePL1 and PpePL15 Are the Core Members of the Pectate Lyase Gene Family Involved in Peach Fruit Ripening and Softening

“…As one of the Cell wall-modifying enzymes, PL genes have been associated with the ripening of banana fruit as high levels of PL transcript accumulate predominantly in ripe fruit but not in unripe fruit (Pua et al, 2001;Marin-Rodriguez et al, 2003). Pectate lyase activity increased during fruit ripening in strawberry (Jimenez-Bermudez et al, 2002;Benitez-Burraco et al, 2003;Zhou et al, 2016), tomato (Uluisik et al, 2016;Yang et al, 2017), and peach (Ortiz and Lara, 2008). However, only a few PL genes were expressed in mature fruit.…”

Fruit softening: evidence for pectate lyase actionin vivoin date (Phoenix dactylifera) and rosaceous fruit cell walls

“…A ripening-related increase in extractable PL activity, assayed in vitro , was reported in many fruits including tomato ( Uluisik et al , 2016 ), banana ( Marín-Rodríguez et al , 2003 ) and strawberry ( Zhou et al , 2016 ). A suggestion that endogenous PL may exhibit action in vivo comes from the observations that, in PL-silenced tomato fruits, less pectin became soluble ( Yang et al , 2017 ) and its molecular weight remained relatively high ( Uluisik et al , 2016 ).…”

“…non-hydrolytically) to give a product with a 4-deoxy-β- l - threo -hex-4-enopyranuronosyl residue (abbreviated as ΔUA, for ‘unsaturated uronic acid’) at the newly formed non-reducing end ( Fig. 1B , reaction i) ( Fuchs, 1965 ; Shaligram and Singhal, 2010 ; Nasuno and Starr, 1967 ; Iqbal et al , 2016 ; Zhou et al , 2016 ). (Note: rules of carbohydrate nomenclature dictate that a β- l -ΔUA residue is the product expected when a lyase catalyses an elimination reaction starting with a pectic α- d -GalA residue; this does not imply any change in the configuration at carbon-1.)…”

“…A putative PL gene was ascribed a possible role in softening ( Jiménez-Bermúdez et al , 2002 ; Marín-Rodríguez et al , 2002 ). PL activity (assayed in vitro ) is extractable from ripening strawberry ( Zhou et al , 2016 ), banana ( Marín-Rodríguez et al , 2003 ) and several other fruits ( Wang et al , 2018 ).…”

Cloning and Functional Identification of SlPG49 in Solanum lycopersicum

“…Four pectin-hydrolytic enzymes involved in pectin modification and degradation have been identified, namely pectin methylesterases (PMEs), pectin acetylesterases (PAEs), polygalacturonases (PGs), and pectate lyases-like (PLLs) [11][12][13][14], which participate in different processes of pectin degradation. PMEs are responsible for the removal of methyl ester groups from pectin [15]; PAEs can cleave the acetylester bond from pectin [16,17]; PGs cleave the α- (1,4)-galacturonosyl linkages in pectin [18]; PLLs can hydrolyze D-galacturonic acid in pectin through a β-elimination reaction [19,20]. The PG family of pectin-hydrolytic enzymes has been known to function in plant growth and development for three decades [21].…”