Peach is the third largest deciduous fruit tree in China, its output and consumption are in the forefront of the fruit industry in north China. Organic acid content is an important component of fruit flavor quality. Previous studies revealed that the peach fruit acidity was controlled by the D (Doux, which means ‘sweet’ in French) locus with a large effect on titratable acidity (TA) or pH value. However, the major gene at locus D has not been revealed before. 

Associate Prof. WANG Lu from the Molecular Breeding of Fruit Crops Group, led by Prof. HAN Yuepeng of Wuhan Botanical Garden, researched on peach acidity trait, and verified the method of dividing peach cultivars into two major categories: the non-acid type and acid type, by the fruit juice pH threshold of 4.0.   

Researchers fine-mapped the D locus on chromosome 5 top using the peach hybrid population, and located the acidity key gene at the top of the chromosome 5th 694 kbp to 1212 kbp position.    

In combination with the analysis of fruit development stage transcriptomes of multiple peach varieties, study found that there was a significantly differentially expressed gene PpRPH in this genetic region of peach, which was not expressed in the late fruit development stage of high-acid varieties.  

This gene was constructed into expression vector and transformed into tobacco leaves, and it caused the pH value of leaves increased significantly, while the content of malic acid and citric acid decreased.    

Combined with the above evidences, PpRPH is the most likely acidity regulator gene at D locus.   

"This study will be helpful for understanding the complex mechanism underlying fruit acidity and genetic improvement of fruit acidity in peach,” said Dr. WANG.  

Results were published in Plant Molecular Biology with the titled of “A candidatePpRPH gene of theD locus controlling fruit acidity in peach”. This work was supported by funds received from the National Key R&D Program of China, the National Natural Science Foundation of China and the China Agriculture Research System. 

Figure I: Fine mapping of the acidity gene at D locus; Figure II: Pulp development stages differentially expressed genes of peach non-acid vs acid varieties found by transcriptome analysis; Figure III: PpRPH can increase in pH value and decrease organic acid contents. CK indicated the empty vector as control, OE indicated the overexpression of PpRPH gene (Image by WANG Lu)