QTL dynamics for fruit firmness and softening around an ethylene-dependent polygalacturonase gene in apple (Malusxdomestica Borkh.)

Abstract

Apple fruit are well known for their storage life, although a wide range of flesh softening occurs among cultivars. Loss of firmness is genetically coordinated by the action of several cell wall enzymes, including polygalacturonase (PG) which depolymerizes cell wall pectin. By the analysis of ‘Fuji’ (Fj) and ‘Mondial Gala’ (MG), two apple cultivars characterized by a distinctive ripening behaviour, the involvement of Md-PG1 in the fruit softening process was confirmed to be ethylene dependent by its transcript being down-regulated by 1-methylcyclopropene treatment in MG and in the low ethylene-producing cultivar Fj. Comparing the PG sequence of MG and Fj, a single nucleotide polymorphism (SNP) was discovered. Segregation of the Md-PG1SNP marker within a full-sib population, obtained by crossing Fj and MG, positioned Md-PG1 in the linkage group 10 of MG, co-located with a quantitative trait locus (QTL) identified for fruit firmness in post-harvest ripening. Fruit firmness and softening analysed in different stages, from harvest to post-storage, determined a shift of the QTL from the top of this linkage group to the bottom, where Md-ACO1, a gene involved in ethylene biosynthesis in apple, is mapped. This PG–ethylene-related gene has beeen positioned in the apple genome on chromosome 10, which contains several QTLs controlling fruit firmness and softening, and the interplay among the allelotypes of the linked loci should be considered in the design of a marker-assisted selection breeding scheme for apple texture.

Identification of QTLs for Flesh Mealiness in Apple (<i>Malus</i> × <i>domestica</i> Borkh.)

“…A new strategy for detecting QTLs (e.g., metaQTL analysis) could also be beneficial. Several QTLs for fruit texture and storability traits have been identified on this chromosome (Ben Sadok et al, 2015;Bink et al, 2014;Chagné et al, 2014;Costa et al, 2010;Kenis et al, 2008;King et al, 2000;Kumar et al, 2013;Kunihisa et al, 2014;Longhi et al, 2013b). Our findings confirm the importance of chr 10 for elucidating the regulatory mechanisms of fruit texture and storability.…”

“…The relationships between harvest time, ADM, and genotypes of Md-PG1 SSR 10kd were of interest because QTLs for harvest time and storability traits have been identified in the flanking region of MdPG1 Costa et al, 2010;Kenis et al, 2008;Kunihisa et al, 2014). Weak correlations observed between harvest time and ADM values for the OA (r = −0.39, P < 0.001) and accessions (r = −0.37, P < 0.001) were consistent with the weak negative correlation between harvest time and storability found in a bi-parental population and genetic resources (Nybom et al, 2013).…”

“…To increase the power of GWAS, the sample size should be increased (Korte and Farlow, 2013). In the region near AF057134-SSR, QTLs for fruit firmness at harvest (Costa et al, 2010) and after two months of cold storage (Bink et al, 2014), were identified by bi-parental and pedigree-based QTL mapping, respectively. It is not clear whether the causal gene considered in our study and described in the previous reports is the same; all these studies had a lower marker density and larger confidence interval.…”

“…Simultaneous recordings of mechanical and acoustic parameters allow a comprehensive characterization of flesh texture (Costa et al, 2010). Longhi et al (2012Longhi et al ( , 2013a employed this phenotypic assessment with a quantitative trait locus (QTL) mapping approach using an F 1 population, and an association study using genetic resources.…”

Genome-wide analysis of the RING finger gene family in apple

“…Since the tomato and apple are both climacteric fruit, we first used the heterologous gene expression profiles in tomato fruit development as clues. Costa et al (2010) identified 652 genes differentially expressed during tomato fruit development, and we used these sequences as queries to perform a BLASTN search against all the RING-containing genes in apple. Interestingly, only two putative clusters, SGN-U213593 and SGN-U212955, exhibited similarity with one apple RING-H2 type protein, MDP0000303817, indicating the rarity of differentially expressed RING-containing E3 proteins in apple.…”