Transgenic analysis of tomato endo-β-1,4-glucanase gene function. Role of cel1 in floral abscission

Abstract

Endo-β-1, 4-glucanase (EGase) expression in ripening tomato fruit and abscising tomato flowers reflects the overlapping accumulation of structurally divergent gene transcripts, including EGase1 (Cel1) and EGase2 (Cel2). Transgenic plants in which cel1 expression was specifically inhibited were evaluated in order to assess the potential role(s) played by Cel1 during fruit ripening and floral abscission. The constitutive expression of an antisense cel1 gene driven by the 35S promoter of cauliflower mosaic virus resulted in the reduction of Cel1 mRNA to trace levels in both ripening fruit and abscising abscission zones of transgenic tomato plants. Transgenic fruit in which cel1 expression was reduced to less than 0.1% of wild-type levels exhibited normal growth and softening behaviour. Transgenic floral abscission zones expressing 5-7% of wild-type levels of Cel1 mRNA exhibited an incidence of abscission reduced by up to one third. The incomplete loss of abscission ability by transgenic flowers may indicate that the contribution of Cel1 activity is insufficient to account for all floral abscission and attests to the presence in tomato abscission zones of additional cell wall hydrolase activities, including Cel2.