α-L-arabinofuranosidase activity and gene expression in two tomato cultivars showing different flesh textures

In ripe fruit, depolymerization/solubilization of hemicellulose and pectin is controlled by a set of cell wall-modification enzymes. A decrease of mechanical strength and the determination of flesh texture in the fruit are caused by metabolic changes associated with cell wall polysaccharide. In tomato, it has been shown that pectate lyase has a central role in fruit softening. However, in spite of flesh texture being an important factor in determining fruit quality, little is known about the enzyme(s) relating to the control of flesh texture. Changes in the strength of cell-to-cell adhesion in fruit are considered to be one of the factors involved in changes in fruit texture. Several reports have been shown that arabinosyl-containing polysaccharides play important roles in cellular attachment or cell wall flexibility. α-L-arabinofuranosidase is an enzyme which is capable of releasing arabinofuranosyl residues from polysaccharides. To examine the contribution of α-L-arabinofuranosidase to fruit texture formation, we measured α-L-arabinofuranosidase activity and transcription levels of α-L-arabinofuranosidase-encoding genes in two tomato cultivars: 'Shonan Pomoron Red' and 'Reiyo'. Compared to fruit showing normal texture, a higher activity of α-L-arabinofuranosidase was observed in fruit showing abnormal texture. However, no significant difference in fruit firmness was found between the fruit of the two cultivars. These results indicate that α-L-arabinofuranosidase potentially caused the abnormal flesh texture in tomato fruit. Among six α-L-arabinofuranosidase-encoding genes, the transcripts of two genes were not detected in the both cultivars. Other genes, which showed differential expression patterns, would be responsible for the formation of abnormal flesh texture in tomato fruit.