Fruit shape is one of the most important quality traits of pepper (Capsicum spp.) and is used as a major attribute for the classification of fruit types. Wide natural variation in fruit shape exists among the major cultivated species Capsicum annuum, allowing the identification of several QTLs controlling the trait. However, to date, no genes underlying fruit shape QTLs have been conclusively identified, nor has their function been verified in pepper. We constructed a mapping population from a cross of round- and elongated-fruited C. annuum parents and identified a single major QTL on chromosome 10, termed fs10, explaining 68 and 70% of the phenotypic variation for fruit shape index and for distal fruit end angle, respectively. The QTL was mapped in several generations and was localized to a 5 Mbp region containing the ortholog of SlOFP20 that suppresses fruit elongation in tomato. Virus-induced gene silencing of the pepper ortholog CaOFP20 resulted in increased fruit elongation on two independent backgrounds. Furthermore, CaOFP20 exhibited differential expression in fs10 near-isogenic lines, as well as in an association panel of elongated- and round-fruited accessions. A 42-bp deletion in the upstream region of CaOFP20 was most strongly associated with fruit shape variation within the locus. Histological observations in ovaries and fruit pericarps indicated that fs10 exerts its effect on fruit elongation by controlling cell expansion and replication. Our results indicate that CaOFP20 functions as a suppressor of fruit elongation in C. annuum and is the most likely candidate gene underlying fs10.
The hydrophobic cuticle encasing the fruit skin surface plays critical roles during fruit development and post-harvest. Skin failure often results in the fruit surface cracking and forming a wound-periderm tissue made of suberin and lignin. The factors that make the fruit skin susceptible to cracking have yet to be fully understood. Herein, we investigated two varieties of chili peppers (Capsicum annuum L.), Numex Garnet, whose fruit has intact skin, and Vezena Slatka, whose fruit has cracked skin. Microscopical observations, gas chromatography-mass spectrometry, biochemical and gene expression assays revealed that Vezena Slatka fruit form a thicker cuticle with greater levels of cutin monomers and hydroxycinnamic acids, and highly express key cutin-related genes. The skin of these fruit also had a lower epidermal cell density due to cells with very large perimeters, and highly express gene involved in epidermal cell differentiation. We demonstrate that skin cracking in the Vezena Slatka fruit is accompanied by a spatial accumulation of lignin-like polyphenolic compounds, without the formation of a typical wound-periderm tissues made of suberized cells. Lastly, we establish that skin cracking in chili-type pepper significantly affects fruit quality during post-harvest storage in a temperature-dependent manner. In conclusion, our data highlight cuticle thickness and epidermal cell density as two critical factors determining fruit skin susceptibility to cracking in chili-type pepper fruit.
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