β-Galactosidase and α-L-Arabinofuranosidase Activities and Gene Expression in European and Chinese Pear Fruit During Ripening

Abstract

Substantial decreases in cell wall bound galactosyl and arabinosyl residues are two of the most evident cell wall compositional changes that occur during fruit ripening. The roles of β-galactosidase (β-Gal) and α-L-arabinofuranosidase (α-Af), the enzymes responsible for these respective losses, were investigated and compared in European (Pyrus communis L. 'La France') and Chinese (Pyrus bretschneideri Rehd. 'Yali') pear fruits which exhibit different softening characteristics during ripening. The increase in the activities of β-Gal and α-Af during ripening in both types of pear fruit correlated well with an increase in climacteric ethylene production, and a concomitant decrease in flesh firmness in 'La France' fruit. However, there was no noticeable decrease in 'Yali' flesh firmness even after 28 days of storage at room temperature. In both fruit types, enzyme activity and the accumulation of transcripts hybridizing with PpGAL1, PpGAL4, PpARF2, and PcARF1 increased with fruit ripening. Increases in gene expression and enzyme activities in 'Yali' fruit with no detectable softening during ripening indicate that β-Gal and α-Af may not mediate difference in fruit softening between two pears, but that they could play some role(s) in cell wall changes, perhaps in cooperation with other cell wall-modifying enzymes such as polygalacturonase.

Transcriptome Analysis and Ultrastructure Observation Reveal that Hawthorn Fruit Softening Is due to Cellulose/Hemicellulose Degradation

“…In galactose metabolism, β -GAL was usually proposed to modify the cell wall via the removal of galactosyl and arabinosyl residues from polysaccharides in the cell wall at the initiation of fruit ripening ( Mwaniki et al, 2007 ; Martínez and Civello, 2008 ; Chávez Montes et al, 2008 ; Posé et al, 2013 ). High β -GAL activity is very important during early ripening of Jonagold apples ( Gwanpua et al, 2014 ), which is supported by our results.…”

“…Another glycosidase, α -ARF , has been well documented for its involvement in cell wall modifications during fruit ripening. α -ARF has been proposed to release arabinosyl residues from the pectic fraction, and its functions have been widely discussed in melon ( Nishiyama et al, 2007 ), apple ( Ireland et al, 2014 ), and pear ( Mwaniki et al, 2007 ). However, the patterns of α -ARF expression were similar to those of PG1 in this study, indicating that this enzyme is not part of the softening process.…”

Opposite Accumulation Patterns of Two Glycoside Hydrolase Family 3 α-L-Arabinofuranosidase Proteins in Avocado Fruit during Ripening

“…In contrast, the 68 kDa protein showed a temporary accumulation in response to ethylene. The increase may be due to the elevation in the mRNA level; an up-regulation of α-L-arabinofuranosidase genes with ethylene action have been shown in peach and pear fruit (Hayama et al, 2006;Mwaniki et al, 2007). To date, only a cDNA clone encoding α-L-arabinofuranosidase has been isolated from avocado fruit (PaArf/Xyl3A) and the expression was observed in the fruit right after harvest when the ethylene production was still undetectable (Tateishi et al, 2015).…”

“…The members in the families show characteristic gene expression patterns and differential enzymatic properties (Minic and Jouanin, 2006;Tateishi, 2008). Since many ripening-related genes are induced by the ethylene signal, the effect of ethylene treatment on α-Larabinofuranosidase expression, particularly at the transcriptional level, has been extensively studied (Hayama et al, 2006;Mwaniki et al, 2007;Storch et al, 2015;Yoshioka et al, 2010). In many cases, however, it appears that the gene expression is not specifically regulated by ethylene or a ripening signal.…”

“…For example, three family 51 α-L-arabinofuranosidase genes (FaAra1-3) have been isolated from non-climacteric strawberry fruit (Fragaria × ananassa) and their gene expressions increased during ripening, but the transcripts could be also detected in immature fruit (Rosli et al, 2009). Although ethylene-dependent increases in expression of a family 51 α-L-arabinofuranosidase gene (PcARF1) have been observed in both European and Chinese pears (Pyrus communis and P. bretschneideri, respectively), the transcripts were also detected in the fruit before ripening (Mwaniki et al, 2007). As for family 3 α-L-arabinofuranosidase, PpARF/XYL from peach (Prunus persica) fruit has been shown to be upregulated during ripening and a higher concentration of ethylene promoted elevation of the transcript level (Di Santo et al, 2009;Hayama et al, 2006), but the gene was also expressed in the vegetative organs in which ethylene production was barely detectable (Di Santo et al, 2009).…”