Apple (Malus × domestica Borkh.), a member of the Rosaceae family, is one of the most widely cultivated fruit crops in the world. The Proanthocyanidins (PAs) are the major component of phenolics in apple, but mechanisms involved in PA biosynthesis remain unclear. 

Under the supervision of Prof. HAN Yuepeng from Wuhan Botanical Garden, assistant Prof. LIAO Liao investigated the relationship between the PA biosynthesis and the expression of genes encoding leucoanthocyanidin reductase (LAR) and anthocyanidin reductase (ANR) in fruit skin of one apple cultivar and three crabapples. 

Previous research has investigated the functionality of ANR gene family in apple, which was composed of one MdANR1 gene on chromosome 10 and two allelic MdANR2 genes (MdANR2a and MdANR2b) on chromosome 5 (Han et al. 2012). In this study, the role of LAR genes in PA biosynthesis in apple was further reported. Expression profiles of both LAR and ANR genes were investigated in cultivated and wild apple fruits, and functional characterization was conducted for an apple LAR1 gene via ectopic expression in tobacco.  

Transcript levels of LAR1 and ANR2 genes were significantly correlated with the contents of catechin and epicatechin, respectively, which suggested their active roles in PA synthesis. Ectopic expression of apple MdLAR1 gene in tobacco suppresses expression of the late genes in anthocyanin biosynthetic pathway, resulting in the loss of anthocyanin in flowers. Interestingly, a decrease in PA biosynthesis also observed in flowers of transgenic tobacco plants overexpressing the MdLAR1 gene, which could be attributed to decreased expression of both the NtANR1 and NtANR2 genes. 

This finding is not only helpful for understanding the mechanism of the PA biosynthesis, but it will also aid in future attempts to manipulate PA biosynthesis in apple as well as in other plants. 

This work was supported by the ‘‘863’’ and ‘‘973’’ project of China. Results were published in Frontiers in Plant Science entitled “Molecular characterization of genes encoding leucoanthocyanidin reductase involved in proanthocyanidin biosynthesis in apple”.  

Ectopic expression of MdLAR1 gene resulting in loss of anthocyanin in tobacco (Image by LIAO Liao)