Virus-Induced LeSPL-CNR Silencing Inhibits Fruit Ripening in Tomato

Fruit ripening is a developmentally and genetically programmed process. In tomato (Solanum lycopersicum), ripening determines fruit quality, commodity value, shelf life and many important attributes. To understand this intricate process and its underpinning mechanism, an efficient and effective approach for screening and functional analysis of ripening-associated genes (RAGs) is required. Virus-induced gene silencing (VIGS) is a powerful reverse genetics tool for uncovering gene functions in plants. VIGS has been exploited to investigate roles of RAGs in tomato ripening. However in most cases, virus-induced RAG silencing is only assessed and correlated with the chromatic change of fruits. Here we report that silencing of LeSPL-CNR through a Potato virus X-based VIGS inhibited fruit ripening and led to development of non-ripening sectors in Ailsa Craig (AC) tomatoes. Non-ripening sectors remained firmer and possessed greater relative electric conductivity and acidity as well as a higher amount of chlorophyll, but a lower quantity of anthocyanin. VIGS of LeSPL-CNR also affects expression of other key RAGs and genes associated with biogenesis of ripening hormone ethylene. These findings indicate that AC fruits undergoing VIGS of LeSPL-CNR phenocopied physical, physiological, agrochemical, biochemical and molecular characteristics of the Colourless non-ripening epimutant. Thus, the overall phenotypical changes from visual appearance to RAG expression caused by LeSPL-CNR silencing reaffirm the great usefulness of VIGS to reveal biological functions of genes crucial in tomato ripening and fruit quality.