Fuente: WIPO "tomato" Disclosed are a polynucleotide, a protein, a biological material, and use thereof in the improvement of the quality of a plant fruit. The polynucleotide includes any one of the sequences set forth in SEQ ID NOs: 3, 11, 23-36, and 95-108; a complementary sequence, a degenerate sequence, or a homologous sequence thereof; a sequence hybridized with the sequence or a complementary sequence thereof under rigorous conditions; and a cDNA sequence of the sequence. It is found that the gene is a key regulatory gene affecting the sugar content of the fruit, and in the use, the content of SSC, glucose, fructose, citric acid, and malic acid of the plant fruit can be regulated by regulating the protein function, the expression level, and the like of CDPK gene without significantly affecting the weight of the fruit, such that the quality and flavor of a tomato fruit are improved.