Isolation and Characterization of A Cytosolic Pyruvate Kinase cDNA From Loquat (Eriobotrya japonica Lindl.)

Pyruvate kinase catalyzes the final reaction of glycolysis, and plays an important role in controlling glycolytic flux. In this study, a full-length cDNA of a putative Eriobotrya japonica Lindl. (loquat) pyruvate kinase, designated EjPK, was isolated. The nucleic acid sequence of EjPK shares about 78-84 % similarity with already studied plant cytosolic pyruvate kinases. EjPK belongs to the cytosolic-1 subgroup of pyruvate kinase, which includes grape, soybean, and citrus cytosolic pyruvate kinases. The cytosolic localization was confirmed by confocal microscopy using transiently expressed 35S:EjPK-GFP fusion protein. Real-time RT-PCR indicated that EjPK is expressed in loquat leaves, roots, stems, flowers, and fruits. Loquat fruits ripen in two stages: in the first stage, the acid content increases, and in the second stage, acids are consumed and at the same time sugars accumulate. EjPK displayed a remarkable expression pattern in the developing fruit as EjPK transcripts increased dramatically and transiently during the transition period between the two stages. The burst of EjPK mRNA expression had greater intensity in a loquat cultivar displaying higher fruit sugar content than in a cultivar with lower fruit sugar concentration. A potential regulatory role of EjPK in loquat fruit ripening is proposed.