Transcriptomic Analysis of Cold Induced, Ripening-Related, Gene Expression in 'Bartlett' and 'D'Anjou' Pear Fruit

European pears (Pyrus communis L.) require a range of cold-temperature exposure to induce autocatalytic ethylene biosynthesis and fruit ripening. While physiological and hormonal responses of pear to cold-temperature storage have been well characterized, the molecular mechanisms underlying this phenomenon are not yet well understood. We investigated the response of ‘D’Anjou’ and ‘Bartlett’ pear at four different physiological stages during the cold conditioning process. Following total RNAseq and transcriptome assembly, we conducted a functional annotation of all expressed contigs using Blast2GO. We then conducted time course differential expression analysis using the maSigPro R package, by which we identified four distinct clusters of differentially expressed genes and associated ripening-related signaling pathways of hormonal and environmental nature. In addition to validating expression patterns of known ripening-related genes, we also identified a number of genes associated with vernalization, a well-studied processes whose initiation is also dependent on accumulation of chilling hours. These genes, previously implicated in transition from vegetative to reproductive state in flowers, include VIN3, COLs, histone lysine methyltransferases, and other genes associated with chromatin modification. By analyzing expression patterns of putative cold-responsive genes, we lend support to the hypothesis that achievement of ripening competency in pear is a process whose underlying mechanisms parallel those of vernalization. Taken as a whole, the data provide insight into the mechanisms of cold-induced transcriptional regulation of ripening and further elucidate points of regulatory control of ripening in European pear.