Chicken H/L Selection Effect Analysis And Functional Gene Screening

Disease resistance breeding is the research hotspot at present.Due to the difficulty in measuring disease resistance traits and the high cost,it is difficult to identify related disease resistance genes in a genome wide scale.The selection method of disease resistance breeding is still being explored.In this study,the heterophil/lymphocyte?H/L?selection effect was studied by using H/L as the main selection trait,and the relationship between H/L and disease resistance traits was directly identified.Heterophils are immune cells of birds that are resistant to invasion by external pathogens.Previous studies have shown that the ratio of H/L has a significant enhanced ability to resist Salmonella infection.This study will compare the disease resistance index of H/L selection line and randomly select control line under artificial infection conditions and the difference of gene expression in immune organs,analyze and evaluate the breeding effect of H/L line and screen candidate genes.The two experiments mainly included in this study are as follows:Experiment 1:This study was conducted in the H line in experimental base of institute of animal sciences.This line is selected for lower H/L ratio using the family selection method.Each generation has an independent panmixia randomly select line.In the tenth generation,the breeding line?S?and the randomly select line?RS?were used as the experimental group,and the chicks were divided into S and RS groups.There were 116 and 30 chicks in the group respectively.The chicks were infected with Salmonella typhimurium with concentration of 2.5×10 ¹00 cfu/mL.Three days after infection?dpi?,indicators such as mortality and bacterial load were recorded.The results showed that the mortality of the3 dpi S and RS were 12%and 20%,respectively.At 3 dpi,there were significant differences in the liver bacterial load and lysozyme between S and RS?P<0.05?.The chickens in?1?were divided into S and RS line.To verify mortality,there were 35 and 60 chicks in the group respectively,the oral administration of Salmonella typhimurium infection was conducted at 7-day-old chicks,and the concentration of bacteria was 5×10 ⁹ cfu/mL.Mortality was recorded 3 days after infection.The mortality rates of S and RS line were 2.80%and 11.60%at 3dpi,showing significant differences?P<0.05?.The tenth generation of the H/L line was used as the test group?first infection test group?.In RS line,9 chicks with significant differences in bacterial load were selected,and spleen,cecum,cecal tonsil and bursa of Fabricius were collected for transcriptomics.The results showed that there were lots of differentially expressed genes in the two groups,and the number of differentially expressed genes of cecal tonsil and spleen tissues were6413 and 5833,respectively.A total of 19 genes were significantly different among the four immune tissues,mainly including heat shock protein family related genes?HSP90AA1,HSPH1,HSPA8,HSPA5,HSP90B1,HSPA4L,DNAJA1 and HYOU1?,which were significantly increased in S line.Experiment 2:Using the rapid-type white feather broiler B line as the material,the genome-wide association analysis of H/L was performed using a 55K SNP chip.The number of samples was 1,650 42-day-old chickens,and H/L values are tested.The P value was corrected using the LD-corrected Bonferroni method.The corrected 5%genome significant level P value threshold was 2.42×10^-6,and the potential correlation P value threshold was 4.83×10^-5.Our results showed that there were two SNP loci that were significantly associated with H/L,include CARD11,BRIX1(P<2.42×10^-6).In this study,important differential genes such as HSPH1,HSPA8 and HSPA5 were screened by H/L selection line selection and transcriptome sequencing;two important candidate genes for CARD11 and BRIX1 were identified by genome-wide association analysis of white feather broilers.The results of group sequencing and genome-wide association analysis showed that CARD11 and BRIX1 were differentially expressed in spleen,CARD11 and BRIX1 could be used as important candidate genes for H/L selection.