Apple is a widely cultivated fruit crop in the temperate zone. Apple fruits are an important source of phenolic compounds, including flavonoid and chlorogenic acid (CGA), which are associated with health benefits, especially in the prevention and treatment of cardinal vascular diseases. However, the mechanism underlying CGA accumulation in apple fruits remains elusive. 

Supervised by Prof. HAN Yuepeng from Wuhan Botanical Garden of the Chinese Academy of Sciences (CAS), assistant Prof. LIAO Liao has identified two candidate genes that played important roles in CGA accumulation in apple fruits according to comparative transcriptome analysis between high- and low-CGA accessions.     

According to the researchers, a wide variation in CGA content was observed in both cultivated and wild apples according to a measurement in mature fruits of 379 apple accessions, and the average CGA content was significantly higher in cultivated apples than that in wild apples, which suggested that CGA content has undergone selection during apple domestication.   

Moreover, CGA was primarily synthesized via the caffeoyl-CoA and quinic acid route, while the lack of homolog encoding quinate hydroxycinnamoyl transferase in the apple genome suggested the absence of CGA formation via caffeoyl glucoside and quinic acid.  

Additionally, the researchers revealed that the transcriptional levels of two structural genes, MdPAL3 and MdHQT, were significantly correlated with CGA contents, suggesting their crucial roles in determining CGA accumulation in apple fruits.   

This work provides insights into the mechanism underlying fruit CGA accumulation in apple, which could be helpful for development of functional apples with high CGA content in future apple breeding programs. 

Results have been published in Journal of Food Composition and Analysis entitled "Evaluation of chlorogenic acid accumulation in cultivated and wild apples."  

This study was supported by grants from the National Natural Science Foundation of China, the Special Fund for Strategic Pilot Technology of CAS, and the Overseas Construction Plan for Science and Education Base, China-Africa Center for Research and Education of CAS.

Expression patterns of genes involved in a proposed pathway of chlorogenic acid biosynthesis at three developmental stages in wild and cultivated apples. (Image by LIAO Liao)