Lipid-Related Domestication Accounts for the Extreme Cold Sensitivity of Semiwild and Tropic Xishuangbanna Cucumber ( L. var. ).

Xishuangbanna (XIS) cucumber ( L. var. ) is a semiwild variety originating from low latitude tropic areas, and therefore shows extreme cold sensitivity and heat tolerance. Here, we mapped the quantitative trait loci (QTLs) that control the cold sensitivity and heat tolerance of XIS cucumber seedlings. Using bulked segregant analysis (BSA), we identified three QTLs (, , and , with a total length of 11.98 Mb) for heat tolerance and two QTLs ( and , with a total length of 8.74 Mb) for cold sensitivity. The QTL was then narrowed down to a length of 641 kb by using kompetitive allele-specific PCR (KASP) markers. Based on structural variants (SVs) and single-nucleotide polymorphisms (SNPs), we found the is covered by a high divergent region including a 50 kb deletion in the XIS49 genome, which affects the gene structure of lipase (, Csa_6G032560). Accordingly, there is a very big difference in lipid composition, but not in other osmoprotectants like free amino acids and fatty acids, between XIS49 and cultivated cucumber CL. Moreover, we calculated the composite likelihood ratio (CLR) and identified selective sweeps from 115 resequencing data, and found that lipid- and fatty-acid-related processes are major aspects in the domestication of the XIS group cucumber. is a particularly special region positioned nearby lipid-related selective sweeps. These studies above suggested that the lipid-related domestication of XIS cucumbers should account for their extreme cold sensitivity.