Transcriptional analysis of cell wall and cuticle related genes during fruit development of two sweet cherry cultivars with contrasting levels of cracking tolerance

Rain-induced cracking before harvest is the major cause of crop loss in sweet cherry (Prunus avium [L.] L.) In order to better understand the relationship between cherry fruit cracking and gene expression, the transcriptional patterns of six genes related to cell wall modification and cuticular wax biosynthesis were analyzed during fruit setting (FS), fruit color change (FC) and fruit ripening (FR), employing two contrasting cultivars: the cracking resistant 'Kordia' and the cracking susceptible 'Bing'. The transcription levels of AP2/EREBP-type transcription factor (PaWINB), wax synthase (WS), s-ketoacyl-CoA synthase (PaKCS6), and s-galactosidase (s-Gal) showed higher levels in 'Kordia' than in 'Bing' during the FS stage, while similar values were observed in both cultivars at FR stage. In contrast to that pattern, transcription levels of expansin (PaEXPl) were higher at FR stage in 'Kordia' than in 'Bing'. Transcript profile of lipid transport protein gene (PaLTPGl) decreased during fruit development, with higher levels in 'Bing' than in 'Kordia' at FC and FR stages suggesting no relation with cracking tolerance. The expression profiles of PaWINB, WS, PaKCS6, and s-Gal suggest that they are genes involved in conferring cracking tolerance, likely due to their function in cuticle deposition during early stages of fruit development. In addition, a greater expression level of expansin gene would allow for a faster growth rate in 'Kordia' at FR stage.