| Babylonia areolata is an important economically cultivated shellfish,mainly distributed in Thailand,Vietnam and the southeastern coastal areas of China.At present,the main culture area of B.areolata in China is in Hainan,and the main cultured species are Thailand and Hainan populations,of which the former is the main one.In recent years,the frequent occurrence of diseases has severely restricted the healthy development of B.areolata breeding industry.Therefore,it is necessary to carry out trait analysis and genetic improvement of the existing germplasm resources of B.areolata,and to cultivate new species with high resistantce to stress or disease.In crossbreeding research between Thailand and Hainan populations of B.areolata,we found that the growth and survival indicators of their F1 hybrids showed heterosis during the grow-out period,but the physiological basis and molecular mechanism of heterosis for survival rate are still lacking.In order to understand and utilize heterosis more clearly,this study starts from physiology and molecular biology analysis,focusing on the stress and disease resistance traits of B.areolata,conducted comprehensive analysis and comparison among Thailand(TT)and Hainan population(HH)of B.areolata and their reciprocal crossing(TH,HT).The main results are as follows:1.Microsatellite analysis of genetic diversity and genetic structure of different populations and hybrids of B.areolata.The genetic structure changes of Thailand population(TT),Hainan population(HH),Zhanjiang population(ZJ),Zhao’an population(ZA)and Changle population(CL)of B.areolata were studied by microsatellite makers.In addition to CL and ZA,there was significant genetic differentiation among other populations.Genetic structure analysis also showed that CL,ZA,and ZJ were closely related,and were significantly different from HH and TT,there was also a significant difference between HH and TT.Based on microsatellite markers,the genetic diversity and genetic differentiation of TF4,TF5 and TF6 in selective breeding populations of Thailand were studied.The results showed that the three consecutive breeding generations still maintained high genetic diversity,weaker genetic differentiation,and similar genetic background and structure,indicating that the selective breeding in large populatin had a weak influence on the genetic variation and differentiation in the three generations of TF4,TF5,and TF6.The results of genetic structure analysis in Thailand population and Hainan population of B.areolata and their hybrids showed that compared with parental selfreproducing populations,the genetic diversity of hybrids was increased,and the genetic differentiation of hybrids was the lowest,and genetic structure was significantly different from their parents.This indicated that the crossing between Thailand population and Hainan population had produced a certain genetic variation in their hybrids.2.Analysis of stress resistance and nutrient composition in Thailand and Hainan populations of B.areolata and their hybridsThe Arrenius break of temperature(ABT)as heart rate of babylonia increased in rising temperature and the babylonia zero temperature(BZT)as heart rate of babylonia decreased in cooling were used as indicators to evaluate the tolerance ability of B.areolata to high and low temperature separately.Results found that both TH and HT showed heterosis in low temperature tolerance trait,indicating that hybridization improved the ability of hybrids to low temperature tolerance.Among them,HT has a stronger tolerance to low temperature and has a certain best-parent heterosis in low temperature tolerance.However,the ability of hybrids to high temperature resistance was not improved.The survival rate of TT,TH,HT and HH under low-salt stress were measured.Results showed that under the conditions of 27.5℃ and 12 ppt,the LT50 of TH and HT after 72 h in low-salt stress were both significantly larger than HH,indicating that TH and HT have a survival advantage over HH at low salt.Among them,the advantage of TH was slightly stronger,and it has obvious middle-parent heterosis.The LT50 and oxygen consumption rate of TT,TH,HT and HH under acute hypoxia stress were measured,and results showed that hybrid progeny did not show heterosis in hypoxia tolerance.A comparative study on nutritional components of foot muscle and liver in TT,TH,HT,and HH was carried out.The results showed that in muscle,the glycogen and crude fat content of TH and HT showed obvious best-patent heterosis,and the EPA+DHA content of TH and the delicious amino acid(DAA)content of HT showed a certain middle-parent heterosis and best-parent heterosis,respectively.In liver,the crude protein content of TH and HT showed a certain best-parent heterosis.That the EPA+DHA content of HT,the total amino acids(TAA),essential amino acids(EAA)and umami amino acids(DAA)content of TH and HT also showed a certain best-parent heterosis.3.Comparison of immune response characteristics among Thailand and Hainan populations of B.areolata and their hybridsAt 27.5℃,Vibrio harveyi were injected into the muscle of TT,TH,HT and HH.It was found that the LC50 of 4 populations after infection with pathogenic bacteria 48 h and 72 h showed HH-LC50>HT-LC50>TH-LC50>TT-LC50,HT has stronger middleparent heterosis against vibrio.Change of non-specific immune indicators,such as total hemocyte count(THC),hemocyte mortality rate and reactive oxygen species(ROS)of TT,TH,HT and HH,showed that under normal conditions,HT had higher level THC and maintained it throughout the infection process,while HT and HH showed significantly lower hemocyte mortality rate and higher ROS level.Above results indicated the heterosis of HT for disease resistance,which may be mainly because it inherited the more efficient non-specific immune function from HH.The changes of pathogen amount in hemolymph of TT,TH,HT and HH during the process of infection with pathogenic bacteria were measured.After infection with pathogen,the pathogen amount in hemolymph of 4 populations increased sharply to the highest value and then slowly decreased.Compared with their control group,the change rates of cumulative total pathogen content in hemolymph of 4 populations after being infected with pathogenic bacteria at 6 time points,including 0 h,6h,12 h,24 h,36 h,48 h and 72 h,were 114.81%,111.14%,90.39%,and 95.79%,respectively,indicating that HT could more efectively exert innate non-specific immune function to suppress and eliminate pathogenic microorganisms in body after infection with pathogenic bacteria.4.Transcriptomics study on heterosis of disease resistance in hybrid of B.areolataResults of transcriptomics analysis showed that the overall genes expression pattern of HT under pathogen infection was biased towards HH.311,917,and 366 nonadditively expressed genes(NAG)were identified at 3 time points(0 h,12 h,24 h)after pathogen infection,and partial dominance genes accounted for the highest proportion among NAG,reaching 44.60%and 53.83%at 12 h and 24 h,respectively,indicating that the expression level of NAG in HT was mainly between the two parents during the process of pathogen infection.In addition,the gene function analysis of NAG revealed that these genes were mainly involved in immune function,such as immune factor regulation,phagocytosis and clearance of pathogenic bacteria,detoxification and antioxidation,inflammation and apoptosis.Above results indicated intensity of response at related immune gene in HT was weak than the susceptible TT under pathogen infection,indicating that HT could more effectively exert cellular and humoral immune functions to deal with pathogen infection showing a heterosis in disease resistance phenotype.5.Genome-wide association study of hybridation against vibrio in B.areolataUsing whole-genome resequencing technology,the disease resistance trait of HT family population was analyzed through genome-wide association study.A total of 44 significant SNPs was identified,and 19 candidate genes were involved.Among them,birc2,casp8,sbk1,irf2 and pparg were closely related to the immune response.Except for pparg,the other four genes also showed non-additive expression after pathogen infection 12 h in HT.The above genes could be used as important candidate genes for studying the role of heterosis of disease resistance in B.areolata hybrid. |
PDF Full Text Request