Transcriptomic profiling of the walnut endopleura during its development

The color of endopleura is one of the most commercially important characteristics of walnut. There exists one major loci on chromosome 9 significantly associated with the color trait. Zooming in on the GWAS peak region, we found a gene JreChr09G12363 homologous to ANR (BAN) located within this region. ANR encodes an anthocyanidin reductase, which functions as a negative regulator of flavonoid biosynthesis and is involved in procyanidin accumulation in the seed. We further examined the transcriptomic profile of this gene in the endopleura, and found that during the development of endopleura, the expression level of JreChr09G12363 (JrANR) showed a continuously increasing trend, and FPKM value could reach up to ~800, providing support for a role of JrANR playing in the endopleura development. Transcriptomic data for walnut endopleura samples were generated in this study. The samples were harvested at 35, 63, 91, 119, 147 days after pollination during the walnut development stage from walnut cultivar ‘Linzaoxiang’ at Chinese Academy of Forestry. At each time point, endopleuras collected from 7 nuts were mixed into one biological replicate, with three replicates at each stage. Total RNA was extracted using the universal total RNA kit (Tiangen, Beijing, China). Transcriptomic sequencing was performed on the NovaSeq 6000 platform at Novogene Company (Beijing, China).