Genetic Mapping Of Genes Controlling Seed Color In Lettuce

Lettuce（Lactuca sativa）seeds have three different types of colos,black,white and brown.The underlying mechanism of seed color has been extensively studied in Arabidopips,soybean and rice,but rarely studied in lettuce.A F₄ RIL（Recombinant Inbred Lines）population was obtained from a cross between lettuce Y37（black seeds）and S1（white seeds）.The population showed segregation of seed color.Two pools were made,one with 37 individuals with black seeds,the other with one for 48 individuals with white seeds.Total RNAs were extracted from the two pools and sent to company for sequencing.The frequencies of the two alleles of each SNP in the two pools was calculated and the allele difference was plotted along lettuce chromosomes.Using BSR-Seq,the plot clearly showed that the gene controlling seed color was located on Chr7,in the interval of 46Mb-55Mb.A large F₂ population was used to fine map the casual gene.Finally,the locus was mapped to the interval 49.16Mb-49.26Mb on Chr7.Ten genes were predicted in this region.The gene LsTT2,which is homologous of Arabidopsis TT2,is considered as the candidate gene controlling the seed color.To map the gene controlling the brown seed color of lettuce,we used a F₂population derived from a cross between lettuce PI251246（brown seeds）and PI358001-1（white seeds）.The population had three types of seed color,black,brown and white.We made two pools,one for black seeds lettuce（20 individuals）,one for brown seeds lettuce（20 individuals）.Total RNAs were extracted from the two pools and sent to company for sequencing.Using BSR-Seq,the plot clearly showed that the gene controlling seed color was located on Chr2 and fine mapped to the interval of 96.24Mb-100.62Mb of Chr2.In the region,we found seven CHS homologues and LG2229551 is considered as the candidate gene.