Comparative transcriptome analysis shed light on C. crenata peelability by CcNST1 network and accumulation of condensed tannins

Korean/Japanese chestnut, Castanea crenata is commonly used as food ingredient due to their nutritional value and sweet taste in Eastern Asia. However, C. crenata has hard shell tissue with pellicle tissue in outer layer which tastes bitter, protecting flesh and embryo tissues. Peelablity of shell and pellicle is one of the important traits determining market value and consumer preference of C. crenata cultivar. Breeding effort to develop an easy-peeling chestnut was performed and several cultivars were identified. To identify how outer-layer peelability is regulated, we performed mRNA-sequencing analysis on easy-peeling C. crenata cultivar Porotan and hard-peeling cultivar Tsukuba in outer tissues of early stage. We could identify cell wall related genes were up-regulated while cell division related genes and tannin biosynthetic genes were down-regulated in Porotan. Among those, we could identify expression level of NST1 (NAC SECONDARY WALL THICKENING PROMOTING FACTOR1), which is one of the key genes determining the thickness of the cell wall was up-regulated and several tannin biosynthetic genes were down-regulated in Porotan by in silico analysis and qPCR analysis. Moreover, we measured tannin amounts in 8 cultivars and found out hard-peeling cultivars tend to contain more condensed tannin. Thus, we found out outer-layer peelability is dependent on dual gene network which regulates condensed tannin amount and fruit dehiscence.