Pepper β-galactosidase 1 (PBG1) plays a significant role in fruit ripening in bell pepper (Capsicum annuum)

Abstract

During bell pepper (Capsicum annuum L.) fruit ripening, β-galactosidase activity increased markedly as compared with other glycosidases. We purified 77.5 kDa exo-1,4-β-D-galactanase from red bell pepper fruit classified as β-galactosidase II. A marked decrease in galactose content appeared during fruit ripening, especially in the pectic fraction. The purified enzyme hydrolyzed a considerable amount of galactose residues in this fraction. We isolated bell pepper β-galactosidase (PBG1) cDNA. This PBG1 protein contained the putative active site, G-G-P-[LIVM]-x-Q-x- E-N-E-[FY], belonging to glycosyl hydrolase family 35. Quantitative RT-PCR revealed that the expression of PBG1 in red fruit was significantly stronger than that from any other tissues. Moreover, expression of PBG1 occurred prior to that of pepper endo-polygalacturonase 1 (PPG1), the major fruit-ripening enzyme. Based on these results, it appears that the hydrolysis of galactose residues in pectic substances is the first event in the ripening process in bell pepper fruit.