Phenotype and transcriptome analysis identify the key genes controlling seed size and oil accumulation in oil-Camellia.

Abstract

Key message: Phenotypic analysis of an F1 oil-Camellia population, combined with transcriptome sequencing of its parental lines, identifies pivotal genes controlling seed size and oil accumulation. Oil - Camellia is a major oil-producing tree, known for its high nutritional value and health benefits. Improving seed size and oil content is the key breeding objective, governed by intricate genetic networks. However, the molecular mechanism underlying these traits in oil-Camellia has been rarely reported. In this study, an F₁ population was developed from two parental genotypes, CL4 (hexaploid with high oil content and large seed size) and XG (tetraploid with low oil content and small seed size), which exhibited significant variation in yield-related traits. Ploidy analysis of progenies of F₁ population showed that most individuals were tetraploids and hexaploids, with a smaller number of diploids and octoploids present. Additionally, the analysis identified progeny individuals exhibiting both large seed and high oil content although no clear correlation with ploidy was observed. Comparative RNA sequencing (RNA seq) of developing seeds at four developmental stages revealed dynamic expression patterns, associated with seed size and oil content in the two parents. Co-expression regulatory network and differentially expressed genes of fatty acid biosynthesis pathway indicated that genes, such as Oleosin5 and ACCase α-subunit, displayed central roles in controlling seed size and oil content with notable expression peaks in S3 and S4. Additionally, the ABA signaling pathway, along with expansin proteins and transcription factors, showed co-expression with these genes, suggesting a regulatory pathway centered around Oleosin5 and ACCase α-subunit. This study identifies essential genes linked to oil seed yield traits, enhancing the understanding of oil-Camellia's molecular breeding targets.