Peach, Prunus persica(L.) Batsch, is native to China and now becomes popular worldwide. Based on the flesh color, peach cultivars can be classified into three groups: white, yellow and blood. Recently, several studies have revealed that the yellow-flesh trait is controlled by a single gene encoding carotenoid cleavage dioxygenase in peach. However, the molecular mechanism underlying the blood-flesh trait remains unclear. 

Under the supervision of Prof. Han Yuepeng, PhD student Zhou Hui from Wuhan Botanical Garden investigated the genetic and molecular mechanism of high content anthocyanin accumulation in blood peach cultivar ‘Dahongpao’. 

Fruits of ‘Dahongpao’(DHP) accumulated high content of anthocyanin (cyanidin-3-glucoside) at fruit ripening stage. Expression profiling of genes involved in anthocyanin biosynthesis in developing fruit showed that all the structure genes were highly expressed at fruit ripening stage in ‘Dahongpao’ but not in white flesh cultivar ‘Baifeng’. These results suggested that anthocyanin biosynthesis in peach fruit was regulated at the transcriptional level. 

The researchers further examined the expression profiles of anthocyanin regulatory genes in developing fruit and found expression level of an R2R3 -type transcription factor (TF) PpMYB10.1 accorded with the color changes in peach fruit. Functional analysis showed that PpMYB10.1 could induce accumulation of anthocyanin, however genetic analysis in across between the DHP and Jinhuadabaitao (JH) cultivars showed that it was not responsible for the blood-flesh trait in peach. 

Genetic mapping in the cross between DHP and Shuguang (SG) anchored the candidate gene in a 200 Kb region at the top of linkage group 5. Combining with Illumina RNA -Seq technology, a candidate gene named Blood (BL) was obtained in that region. It has been reported that NAC proteins form homodimers or heterodimers for their transcriptional activities. Five other NAC genes with high expression level were obtained from RNA-Seq libraries, named NAC1~5 respectively. Dual luciferase assay showed that only NAC1 was the potential partner of BL. The interaction of BL and NAC1 was further verified by Yeast-Two-Hybrid assay and firefly luciferase complementation assay. 

Furthermore, a gene named SPL1 was obtained according to its expression profile in RNA-Seq libraries, and was identified as a repressor for anthocyanin accumulation in peach fruit by dual luciferase assay. 

 A model of anthocyanin accumulation in blood-fleshed peach was proposed as follow: In    white-fleshed fruits, the expression of PpMYB10.1 cannot be activated due to the lack of expression of the BL gene; in blood-fleshed fruits, BL acts with PpNAC1 to activate the transcription of PpMYB10.1, but their transactivation activity was repressed in the presence of the repressor PpSPL1. 

Results were published in The Plant Journal online entitled “Molecular genetics of blood-fleshed peach reveals activation of anthocyanin biosynthesis by NAC transcription factors”. . This work was supported by the National Basic Research Program of China and the National High Technology Research and Development Program of China.