Heterologous overexpression of apple MdWAPL1 promotes fruit shape and alters fruit quality in tomato

The shape of the apple fruit is one of the most significant economic traits of apples, yet it is frequently influenced by a multitude of factors, which has resulted in a paucity of comprehensive research on this subject. In this study, 248 Malus accessions were used for a genome-wide association study (GWAS) to represent the wide diversity of fruit shape in the domesticated and wild Malus gene pools. An identified potential candidate gene, MdWAPL1, located on chromosome 05 of apple, underpins the genetic diversity of apple fruit shape. Heterologous expressing MdWAPL1 in tomatoes resulted in a higher fruit shape index and weight, which was attributed to a thicker fruit pericarp and larger pericarp cell size. Conversely, heterologous expressing MdWAPL1 in tomatoes did not alter the total soluble solids (TSS), titratable acidity (TA), or TSS/TA levels of the fruits, while affected the fruit firmness of tomato fruits. Additionally, heterologous overexpression of MdWAPL1 resulted in a reduction in the contents of 16 amino acids and GABA in the tomato fruits, while altered the contents of tZR and GA₃ in both tomato and apple fruits. Overall, we have identified a candidate gene, MdWAPL1, that is associated with apple fruit shape and size. This gene has the potential to enhance the efficiency of apple breeding programs in the future.