RNA Sequencing Reveals Transcription Factors and Genes in Phenylpropanoid Biosynthesis That Positively Regulate Size and Weight of Oak Tree Seeds

Acorn size is of great importance, both ecologically and economically. However, the long lifespan is an obstacle to improvement in breeding. Keumsura1ho is a recently bred cultivar of oak (Quercus acutissima Carruth) selected after eight years of selection due to its larger acorns and higher weight compared to the control. In the present study, we investigated the transcriptional mechanisms underlying the outstanding morphological characteristics of Keumsura1ho. For this purpose, one- and two-year-old acorns from the control and Keumsura1ho groups were used for comparative transcriptome analyses of their seeds. Among morphological characteristics, the Keumsura1ho seeds were 18.3% longer than those of the control. Seed width and depth were 33.9% greater than those of the control. In the transcriptome analysis, genes related to seed size were further enriched, with biennial Keumsura1ho showing higher enrichment in comparison to control genes. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis revealed that the upregulated genes of the two-year-old Keumsura1ho seeds showed higher enrichment in phenylpropanoid metabolism compared to the control, with OMT1 and PRXs exhibiting high expression levels. This pathway has a significant impact on seed coat lignification and size in Keumsura1ho. The results of this study will benefit the development of breeding techniques by identifying marker genes for seed size.