Genetic Dissection Of Sex Expression And Studies On The Distribution And Expression Of Genes Related To Sex Determination In Cucumber (Cucumis Sativus L.)

Cucumber (Cucumis sativus L.) is the annual herbaceous crops. Cucumber is one of the important vegetable crops in the world. China has the most area of cucumber cultivation and the highest production in the world. Female flower node proportion is a major factor affecting cucumber yield. Meanwhile, the utilization of gynoecious cucumber lines can greatly simplify the Hybridization. As the complexity of cucumber sex expression and genetic mechanism, the traditional methods of sex control and the gynoecious line breeding are not efficient. Therefore, the further study on the genetic dissection of sex expression and the distribution and expression characteristics of genes related to sex determination in Cucumber(Cucumis sativus L.) is important to fully understand the mechanism of sex formation and accelerate the breeding speed. In addition, it could lay the foundation for the isolation and cloning, in vitro reorganization and genetic transformation of genes on sex determination. The researches was done from three aspects and the results are as follows:1. Two sets of F₂, BC₁P₁, BC₁P₂ population were respectively constructed from the cross combination of gynoecious line 'G5224' and monoecious line 'YX05-3-10', and subgynoecious line '1613EF' and 'YX05-3-10'. Through investigation andχ² test of sex types in segregating population, it was found that both gynoecious and subgynoecious traits were controlled by one pair of incompletely dominant gene. With the help of the major gene and polygene mixed inheritance model from the aspect of quantitative genetics, It was proved that there were polygenes involved in both gynoecious and subgynoecious inheritance. The heritability of major gene of the cross of gynoecious line 'G5224' and monoecious line 'YX05-3-10' was 83.8%, and the heritability of polygenes was 8.5%. The heritability of major gene of the cross of subgynoecious line '1613EF' and monoecious cucumber 'YX05-3-10' was 82.0%, and the heritability of polygenes was 8.6%.2. The distribution of the genes related to sex determination in 78 cucumber germplasm materials of different sex pheynotype was analyzed by specific PCR primers based on the sequences of five genes: CS-ACS1G, CS-AC02, CS-AC03, CS-ERS and CS-ETR2. The results showed that all the 5 genes could be detected in all the cucumber materials. It meant that the five genes were not specific to the gynoecius genotypes. ACC synthase gene was cloned from gynoecious line 'G5224'. BLAST analysis revealed that the sequence was highly homologous to the sequence of CS-ACSIG gene at 99%. The results from some other researchers that CS-ACS1G gene existed only in gynoecious cucumbers were not suitable for cucumber germplasm resources with widely genetic beckground.3. The technique of semi-quantitative RT-PCR was employed to study the expression character of ACC synthase gene CS-ACS1G, ACC oxidase gene CS-AC02, CS-AC03 and ethylene receptor gene CS-ERS and CS-ETR2 at 8 different time after treatment on gynoecious line 'G5224', subgynoecious line '1613EF' and '106BE', monoecious line 'YX05-3-10' and 'Xi Shuang Ban Na cucumber 'BN32'. The results showed that ACC synthase gene CS-ACSIG didn't express in all the 80 samples, which showed that the sex pheynotype at late stage of plant growth was not directly related to whether this gene expressed naturally or not in the early seedling stage. The expression of ACC oxidase genes was mostly transient or intermittent only in gynoecious and monoecious cucumber lines, whichshowed synergies with the gynoecious phenotype. But in the subgynoecious line which was strongly reactive to AgNO3, the expression of the ACC oxidase gene was enhanced. This may be associated with different background and different expression machanisms in different sexual materials. Ethylene receptor gene CS-ERS only showed transient expresstion in the gynoecious cucumber 'G5224' and subgynoecious cucumber '106BE'. AgNO3 significantly inhibited its expression. All these showed Ethylene receptor gene CS-ERS has female-specific relation with the gynoecious trait. Ethylene receptor gene CS-ETR2 expressed in all 80 samples to differnt extent. AgNO3 could inhibit the expression (except '1613EF'), and ethylene could promote its expression. Its expression in 5 materials showed higher relative to the gynoecious trait.Viewing on the genes existed in one material, there were 4 genes expressed in gynoecious line 'G5224', including 2 ACC oxidase genes and 2 ethylene receptor genes, and all of them showed some relation with gynoecious trait. In subgynoecious line '1613EF', CS-ACO2,CS-AC03 and CS-ETR2 genes expressed. In subgynoecious line '106BE', all the 2 ACC oxidase genes and 2 ethylene receptor genes expressed. The change of ACC oxidase genes in the 2 subgynoecious lines showed abnormal relation with sex type, and ethylene receptor genes showed synergies with the gynoecious trait. In the monoecious line 'YX05-3-10', CS-ACO2,CS-AC03 and CS-ETR2 expressed, and all of them showed synergies with the gynoecious plant. In the monoecious cucumbe 'Xi Shuang Ban Na cucumber (BN32)', only CS-AC03 and CS-ETR2 expressed, and their expression was synergic with gynoecious. It could be inferred that each of the 4 sex determination genes mentioned above couldn't has the same effect on and the same synergies with the gynoecious performance; Ethylene receptor gene seemed to play more important role in sex-determination; Different sex-determining genes may be responsible for the different sex type. That is, The phenotypes of different sex may be controlled by the different sex-determining genes.