Genome survey and identification of key genes associated with freezing tolerance in genomic draft of hexaploid wild Camellia oleifera

Camellia oleifera Abel. is the dominant woody oil crop under significant development in China. Wild C. oleifera in Lu Mountain is a valuable genetic resource with strong freezing tolerance. With high-throughput sequencing, the genome of wild C. oleifera in Lu Mountain was analysed and 700.3 Gb clean reads were obtained. The genome of wild C. oleifera was estimated as allohexaploid, and its haplotype genome size was about 2.69 Gb-2.79 Gb, with repeat content of 63.01%-73.02% and heterozygosity of 6.30%-7.43%, belonging to a very complex genome. The genomic draft was assembled that contained a total of 6,952,303 scaffolds with N50 length of 1.23 kb, and the overall length was 2.39 Gb with GC content of 40.87%. In the genomic draft, 1,104,618 SSRs were identified; scaffold1096012 and scaffold1779458 were identified as key genes associated with freezing tolerance combined with the transcriptome data of field plus lab experiments. In this study, the genomic background of hexaploid wild C. oleifera in Lu Mountain was revealed. This lays the foundation for obtaining the high-quality chromosome-level reference genome of wild C. oleifera. The identification of SSRs and key genes associated with freezing tolerance may contribute to the efficient exploration and utilisation of this genetic resource.