The diversity of pathogenesis-related proteins decreases during grape maturation.

It was recently shown that wines contain typically a huge diversity of structurally similar polypeptides that exhibit a high degree of homology to pathogenesis-related (PR) proteins. This observation suggested the existence of one or a few precursors in mature grapes, common to most or all the wine PR proteins. Limited proteolysis and chemical modification of the precursor(s) during fruit ripening and winemaking could then generate the large number of distinct wine polypeptides. However, the patterns of PR proteins extracted from grape berries regularly harvested from the onset of development until maturity did not confirm the previous hypothesis. Two different methodologies, involving 2-D immunoblotting and a combination of FPLC cation/anion exchange chromatographies with 1-D immunoblotting, indicate that the total concentration of PR proteins is increased but its diversity is reduced from the early stages of berry development until maturity. These results indicate that PR proteins are synthesized in a wide variety of forms from the early stages of grape development, eliminating the hypothesis previously formulated on the existence of one or few precursors common to the wine proteins.

Environmental conditions during vegetative growth determine the major proteins that accumulate in mature grapes.

Despite recent reports in the literature that chitinases comprise approximately 50% of the soluble proteins present in mature Vitis vinifera L. (cv. Moscatel) grapes, with the other major proteins being thaumatin-like proteins, a careful inspection of the published data reveals inconsistencies as to which proteins actually accumulate in mature grapes. Mature Moscatel grapes were harvested in the same vineyard in two consecutive years, 1999 and 2000. The grapes exhibited widely distinct polypeptide patterns when analyzed by either FPLC cation exchange chromatography or two-dimensional electrophoresis: whrereas the 2000 grapes possessed a much higher protein content (1.96 versus 1.11 mg g(-)(1) of fresh weight), the 1999 grapes contained a greater heterogeneity of polypeptides. In addition, highly specific antibodies that recognize the pathogenesis-related proteins present in the grapes demonstrated that the 2000 harvest grapes had a wider variety of pathogenesis-related polypeptides. N-Terminal sequencing of the major polypeptides revealed differences in the relative abundance and amino acid sequence of thaumatin-like and osmotin-like polypeptides present in the 1999 and 2000 harvest Moscatel grapes and did not detect the presence of chitinase. As a whole, the data indicate that the expression and accumulation of the major proteins in grapes is essentially determined by the environmental and/or pathological conditions prevailing during grape development and maturation. The potential physiological and technological implications are discussed. The results of the present work suggest that it is not possible to base varietal differentiation of grapes on the profile of the pathogenesis-related polypeptides present in the mature berries.