Temporal expression patterns of fruit-specific α- EXPANSINS during cell expansion in bell pepper (Capsicum annuum L.)

BackgroundExpansins (EXP) facilitate non-enzymatic cell wall loosening during several phases of plant growth and development including fruit growth, internode expansion, pollen tube growth, leaf and root development, and during abiotic stress responses. In this study, we characterized the spatial and temporal expression pattern of C. annuum α- EXPANSINS (CaEXPA) genes. Additionally, we correlated fruit-specific CaEXPA expression with the rate of cell expansion during bell pepper fruit development. ResultsSpatial expression patterns revealed that CaEXPA13 was up-regulated in vegetative tissues and flowers, with the most abundant expression in mature leaves. Expression of CaEXPA4 was associated with stems and roots. CaEXPA3 was expressed abundantly in flower at anthesis suggesting a role for CaEXPA3 in flower development. Temporal expression analysis revealed that 9 out of the 21 genes were highly expressed during fruit development. Of these, expression of six genes, CaEXPA5, CaEXPA7, CaEXPA12, CaEXPA14 CaEXPA17 and CaEXPA19 were abundant 7 to 21 days after anthesis (DAA), whereas CaEXP6 was strongly expressed between 14 and 28 DAA. Further, this study revealed that fruit growth and cell expansion occur throughout bell pepper development until ripening, with highest rates of fruit growth and cell expansion occurring between 7 and 14 DAA. The expression of CaEXPA14 and CaEXPA19 positively correlated with the rate of cell expansion, suggesting their role in post-mitotic cell expansion-mediated growth of the bell pepper fruit. In this study, we also identified high transcript abundance of CaEXPA9 during ripening.ConclusionThis is the first genome-wide study of CaEXPA expression during fruit growth and development. We identified a fruit-specific EXPA that may be important in facilitating cell expansion during growth and cell wall loosening during ripening in bell pepper. These EXPA genes could be important targets for future manipulation of fruit size and ripening characteristics.