Transcriptome and metabolome analyses reveal improvement in blueberry fruit quality by interspecific grafting

Key message Our results from transcriptomics and metabolomics extend the understanding of the consequences of interspecific grafting to improve blueberry fruit quality. Abstract Grafting plays an important role in improving fruit quality and plant stress resistance. The effect of interspecific grafting on fruit quality in ‘O'Neal’ blueberry ( Vaccinium corymbosum L.) was investigated with transcriptomics and non-targeted metabolomics. Fruits were collected from own-rooted ‘O'Neal’ (NO), ‘O'Neal’ grafted on ‘Tifblue’ ( V. virgatum Ait.) (TO), and ‘Anna’ ( V. corymbosum L.) (AO) bushes. The total soluble solids and anthocyanin concentrations, and solid:acid ratio in TO fruits were higher, while the vitamin C level was lower than AO and NO. The metabolic profiling showed that interspecific grafted blueberry had higher levels of sugars such as glucose, maltose, raffinose, myo-inositol, and galactinol, as well as glucose-6-phosphate and trehalose-6-phosphate as compared to intraspecific grafted blueberry. The fruits of TO also showed higher concentrations of secondary metabolites such as catechin, 5,7-dihydroxy-4'-methoxyisoflavone, glycyl tyrosine, and tocopherol, and lower concentrations of tryptophan and phenylalanine as compared to AO. Transcriptomic data showed that not only sugar metabolism-related enzymes such as trehalose-phosphate synthase and galactol synthase but also shikimate-derived metabolism-related enzymes such as flavonoid 3'-monooxygenase, anthocyanidin glucosyltransferase, isoflavone reductase, alcohol dehydrogenase, and aspartate aminotransferase were up-regulated in a comparison of TO/AO. Moreover, sugar signaling-related genes such as 6-phosphofructokinase, bHLHs, MYBs, 1-aminocyclopropane-1-carboxylate oxidase, 1-aminocyclopropane-1-carboxylate synthase, ABC transporter, and malate transporter were also up-regulated in a comparison of TO/AO. Finally, we proposed the hypothesis that sugar signals regulate the accumulation of sugars and organic acids and fruit ripening. These results will provide interesting insights into the interaction of scions on rootstocks and the promotion of blueberry genetic improvement.