Genetic And Molecular Basis Of The Cytoplasmic Male Sterility In Soybean

As an efficient approach for crop yield improvement, the use of hybrid varieties has beena widely used approach in various commercial food crops around the world. Great successhas been achieved in the development of hybrid varieties in several major crops, includingrice and maize. Due to lack of genetic male sterile resources or mutants, soybean is one of afew crop species, in which heterosis has not been exploited to a extent that is practicallyviable until recently. Recently successe in the development of soybean cytoplasmic geneticmale sterile (CMS) lines and their application on the use of heterosis in the crop was achievedin China, which marked the leading position of China in the field in the world. SoybeanCMS lines can be classified into two types according to their origins. RN type is derived from167, while ZD type is from ZD8319. Although these two lines has been used for breeding ofhybrid varieties, limited information is available on their mode of inheritance, the molecularbasis of sterility and its restoration, the genetic markers associated with sterility genes andrestorer genes. In rhis study, RN type CMS lines YA, YB and ZD type lines ZA, ZB and theircorresponding restore lines were used to conduct a series of crosses. By studying thesegregations pattern of the fertilities of F₁, F₂ and the backcrossing progenies, the inheritanceof the RN type and ZD type CMS lines were identified. DNA was extracted from the F₂segregating population and screened with simple sequence repeat (SSR) markers to look forgenetic markers closely linked to the restore gene. Moreover, the mitochondria DNApolymorphisms between the CMS lines and the restorer lines were studied using randomamplification of polymorphic DNA (RAPD) analysis. The results of the study aresummarized as followed. 1. Pollen abortion is an indicator for identifying the male sterile plants. Pollen fertilityof F1 plants from five different crosses, including 167×YB, YA×167, YA×Y12R, ZD8319×ZB, and ZA×ZD8319 were examined. All of the F1 pollen is semi-sterile, which providedevidence that the traits of male sterility in these lines are controlled by a single-genicgametophytic-type system. Investigation of the fertilities of these F2 plants and F1 plantsfrom five three-way crosses, including YA×(167×YB), YA×(YB×167),(YA×167)×YB, ZA×(ZD8319×ZB) and ZA×(ZB×ZD8319) revealed that the male sterile nucleargene rf could not transmit through male gametes. The result provides additional evidencethat the male sterility in both RN and ZD types CMS lines are controlled by a single-genicgametophytic-type system. 2. Analysis on the fertilities of individual CMS plants with different extend of malesterility suggested that soybean male sterility can be affected by environmental variables. Indifferent environmental conditions, the male sterility and fertility can be alternated. Thisalternation can be due to quantitative changes in which the percentage of pollen abortionvaries in different growth years. It can also be due to qualitative change, in which the sterilecytoplasm can be converted into fertile cytoplasm. This type of alternating resulted in theoccurrence of unexpected male fertile plants in the progenies of the sterile lines. Theconverting rates vary in different genotypes. 3. Test crosses using YA and ZA as female parent showed that the sterility of both CMSlines could be restored by restorer lines 167 and ZD8319 and maintained by maintainer lineYB. In addition, similar effect of the test crosses between the two CMS lines and GD589,KN4, JLCMS2-2B, JLCMS2-20B, Jihui 4, Jihui 1, 567666, and Jihui 2 on the fertilitieswere observed, indicating that the two types of CMS lines are controlled by the same geneticsystem. Their maintainer and restorer lines can be shared. 4. It is confirmed that restoration of the fertility of the RN type of soybean CMS line iscontrolled by a single dominant nuclear gene. Two SSR makers, Satt414 and Satt596, whichare genetically linked to the nuclear restorer gene, were selected by screening of 210 pairs ofthe SSR marker. T...