(M.L.); 0000-0002-5725-885X (J.P.); 0000-0001-7707-7776 (J.-P.R.).The plant hormone ethylene plays a key role in climacteric fruit ripening. Studies on components of ethylene signaling have revealed a linear transduction pathway leading to the activation of ethylene response factors. However, the means by which ethylene selects the ripening-related genes and interacts with other signaling pathways to regulate the ripening process are still to be elucidated. Using tomato (Solanum lycopersicum) as a reference species, the present review aims to revisit the mechanisms by which ethylene regulates fruit ripening by taking advantage of new tools available to perform in silico studies at the genomewide scale, leading to a global view on the expression pattern of ethylene biosynthesis and response genes throughout ripening. Overall, it provides new insights on the transcriptional network by which this hormone coordinates the ripening process and emphasizes the interplay between ethylene and ripening-associated developmental factors and the link between epigenetic regulation and ethylene during fruit ripening.As a developmental process, fruit ripening is coordinated by a complex network of endogenous and exogenous cues. Indeed, the making of a fruit is a genetically regulated process unique to plants involving three distinct stages: fruit set, development, and ripening. Fruit development is characterized by a series of developmental transitions tightly coordinated by a network of interacting genes and signaling pathways. Among these, ripening has received the greatest attention from both geneticists and breeders. From the scientific point of view, fruit ripening is seen as a process in which the biochemistry and physiology of the organ are developmentally altered to influence the appearance, texture, flavor, and aroma (Giovannoni, 2004). Since most of the fruit sensory and nutritional quality traits are elaborated at the ripening stage, deciphering the key genetic and molecular factors regulating ripening becomes a major task toward improving overall fruit quality (Carrari and Fernie, 2006). In addition, the control of fruit ripening is also instrumental to maintain the quality attributes of the fruit during the postharvest shelf life.Based on their mode of ripening, fleshy fruits are divided into two categories, climacteric and nonclimacteric, depending on the presence or absence of the climacteric rise in respiration and of autocatalytic ethylene production (Lelièvre et al., 1997). In climacteric fruit, the plant hormone ethylene is the major cue that controls most aspects of ripening. By contrast, the ripening of nonclimacteric fruit does not strictly depend on ethylene, and the nature of the triggers of ripening in this type of fruit remains yet to be elucidated. Since the upstream components of the ethylene transduction pathway are common to all ethylene responses, the apparent simplicity of the ethylene signaling pathway cannot account for the wide diversity of ethylene responses. A plausible hypothesis is that dif...

In plants, genomic DNA methylation which contributes to development and stress responses can be actively removed by DEMETER-like DNA demethylases (DMLs). Indeed, in Arabidopsis DMLs are important for maternal imprinting and endosperm demethylation, but only a few studies demonstrate the developmental roles of active DNA demethylation conclusively in this plant. Here, we show a direct cause and effect relationship between active DNA demethylation mainly mediated by the tomato DML, SlDML2, and fruit ripeningan important developmental process unique to plants. RNAi SlDML2 knockdown results in ripening inhibition via hypermethylation and repression of the expression of genes encoding ripening transcription factors and rate-limiting enzymes of key biochemical processes such as carotenoid synthesis. Our data demonstrate that active DNA demethylation is central to the control of ripening in tomato.active DNA demethylation | DNA glycosylase lyase | epigenetic | tomato | fruit ripening G enomic DNA methylation is a major epigenetic mark that is instrumental to many aspects of chromatin function, including gene expression, transposon silencing, or DNA recombination (1-4). In plants, DNA methylation can occur at cytosine both in symmetrical (CG or CHG) and nonsymmetrical (CHH) contexts and is controlled by three classes of DNA methyltransferases, namely, the DNA Methyltransferase 1, Chromomethylases, and the Domain Rearranged Methyltransferases (5-7). Indeed, in all organisms, cytosine methylation can be passively lost after DNA replication in the absence of methyltransferase activity (1). However, plants can also actively demethylate DNA via the action of DNA GlycosylaseLyases, the so-called DEMETER-Like DNA demethylases (DMLs), that remove methylated cytosine, which is then replaced by a nonmethylated cytosine (8