Characterization of tomato fruit ripening and analysis of gene expression in F₁ hybrids of the <i>ripening inhibitor</i> (<i>rin</i>) mutant

Abstract

The ripening inhibitor ( rin ) mutation of tomato yields non‐ripening fruit, and the gene corresponding to RIN , LeMADS‐RIN , is known to encode a transcriptional factor that controls ripening‐related genes. In this study, to evaluate the heterozygosity effect of rin on fruit ripening, we developed eight F 1 hybrid lines of the rin mutant from various crosses between the lines of the rin mutant and wild type. In the fruit of these F 1 hybrid lines, the shelf‐life was improved, but both the shelf‐life and colouring varied between the lines. We then chose one line of the F 1 hybrids and investigated the physiological and transcriptional properties of the fruit. Compared with the wild‐type parent, this F 1 line showed about half the lycopene content, lower fruit softening and lower mRNA accumulation of the genes that encode phytoene synthase ( Psy ), polygalacturonase ( PG ), β‐galactosidase ( TBG4 ) and expansin ( LeEXP1 ). The characteristic climacteric rise in ethylene production typically observed in the wild‐type parent during fruit maturation was not observed in the fruit of this F 1 line. The genes that encode ethylene biosynthetic enzymes, namely 1‐aminocyclopropane‐1‐carboxylic acid (ACC) synthase ( ACS2 and ACS4 ) and ACC oxidase ( ACO1 ), were, however, significantly expressed in the F 1 hybrid, suggesting that the post‐transcriptional regulator for activating these enzymes is affected by LeMADS‐RIN . These results suggest that the heterologous effect of LeMADS‐RIN in F 1 hybrids affects the gene transcription and activation of ripening‐related factors, resulting in changes in fruit properties, including the extension of the shelf‐life.