Background: Akebia trifoliata (Thunb.) Koidz, a perennial wild woody liana, can be used as biofuel to generate bioenergy, as well as a traditional Chinese medicine plant,and new potential edible fruit crop, due to its high yields in fields, wide adaptability, high economic, medicinal and nutritive values, and tolerance tocultivation conditions. However, the pericarp of A. trifoliata cracks longitudinallyalong the ventral suture during fruit ripening, which is a serious problem that limits its usefulness and causes significant losses in yield and commercial value. Furthermore, there have been no known investigations on fruit cracking and its molecular mechanisms in A. trifoliata .
Results: In this study, the dynamic structural changes in fruit pericarps were observed, revealing that the cell wall of fruit pericarp became thinner, and had reduced integrity, and that the cell walls began to degrade in the cracking fruits compared to those observed in non-cracking fruits. Moreover, analyses of the complementary RNA- sequencing-based transcriptomes and tandem mass tag-based proteomes at different development stages during fruit ripening were performed, and the expression of various genes and proteins was found to be changed after cracking, The mRNA levels of 20 differentially expressed genes and 17 differentially abundant proteins (DAPs) involved in cell wall metabolism were further analyzed; 20 DAPs were also validated through parallel reaction monitoring analysis. Among these, pectate lyases and pectinesterase involved in pentose and glucuronate interconversions, β-galactosidases 2 involved in galactose metabolism, were significantly up-regulated in cracking fruits compared to levels in non-cracking fruits, suggesting that they might play crucial roles in A. trifoliata fruit cracking.
Conclusions: This study provides new insights into the molecular basis of fruit cracking in A. trifoliata fruits and important clues for further studies on the genetic improvement of A. trifoliata and the breeding of non-cracking varieties.