Camellia chekiangoleosa has a higher oleic acid content and a shorter reproductive cycle than typical oil tea plants. It was intensively sampled over six C. chekiangoleosa seed development stages. The content of fatty acids determined by GC showed that the accumulation of fatty acids gradually increased from the S1 to S5 stages, and the maximum concentration was reached in S5. Then, fatty acids declined slightly in S6. The main fatty acid component showed the same accumulation trend as the total fatty acids, except linolenic acid, which remained at a low level throughout seed developmental stages. Changes in the expression of fatty acid accumulation-related genes were monitored using second-generation and SMRT full-length transcriptome sequencing. Finally, 18.92 G accurate and reliable data were obtained. Differential expression analysis and weighted coexpression analysis revealed two "gene modules" significantly associated with oleic acid and linoleic acid contents, and the high expression of ENR, KAS I, and KAS II, which accumulate substrates for oleic acid synthesis, was thought to be responsible for the rapid accumulation of fatty acids in the early stage. The rapid increase in fatty acids in the second stage may be closely related to the synergy between the high expression of SAD and low expression of FAD2. In addition, many transcription factors, such as ERF, GRAS, GRF, MADS, MYB and WRKY, may be involved in the fatty acid synthesis. Our data provide a rich resource for further studies on the regulation of fatty acid synthesis in C. chekiangoleosa.

MADS-box genes encode transcription factors that affect plant growth and development. Camellia chekiangoleosa is an oil tree species with ornamental value, but there have been few molecular biological studies on the developmental regulation of this species. To explore their possible role in C. chekiangoleosa and lay a foundation for subsequent research, 89 MADS-box genes were identified across the whole genome of C. chekiangoleosa for the first time. These genes were present on all the chromosomes and were found to have expanded by tandem duplication and fragment duplication. Based on the results of a phylogenetic analysis, the 89 MADS-box genes could be divided into either type I (38) or type II (51). Both the number and proportion of the type II genes were significantly greater than those of Camellia sinensis and Arabidopsis thaliana, indicating that C. chekiangoleosa type II genes experienced a higher duplication rate or a lower loss rate. The results of both a sequence alignment and a conserved motif analysis suggest that the type II genes are more conserved, meaning that they may have originated and differentiated earlier than the type I genes did. At the same time, the presence of extra-long amino acid sequences may be an important feature of C. chekiangoleosa. Gene structure analysis revealed the number of introns of MADS-box genes: twenty-one type I genes had no introns, and 13 type I genes contained only 1~2 introns. The type II genes have far more introns and longer introns than the type I genes do. Some MIKC^C genes have super large introns (≥15 kb), which are rare in other species. The super large introns of these MIKC^C genes may indicate richer gene expression. Moreover, the results of a qPCR expression analysis of the roots, flowers, leaves and seeds of C. chekiangoleosa showed that the MADS-box genes were expressed in all those tissues. Overall, compared with that of the type I genes, the expression of the type II genes was significantly higher. The CchMADS31 and CchMADS58 genes (type II) were highly expressed specifically in the flowers, which may in turn regulate the size of the flower meristem and petals. CchMADS55 was expressed specifically in the seeds, which might affect seed development. This study provides additional information for the functional characterization of the MADS-box gene family and lays an important foundation for in-depth study of related genes, such as those involved in the development of the reproductive organs of C. chekiangoleosa.