Cytological Observation And SSR Mapping Of Genetic Male Sterile Mutant Induced By Space Flight In Maize

Maize Research Institute of Sichuan Agricultural University (MRI, SAU) sent maizeseeds for satellite abroad in 1996. A male sterile mutant was found among six excellentmaize materials. The primary research indicated that the male sterile trait was governed bya single homozygous recessive gene, and the male sterile gene was located on maizechromosome 3L. In order to determine the cytological mechanism of microspore abortionand the precise location of maize genetic male sterile (GMS) gene, the maize GMSmaterials induced by space flight were used as the experiment objects. This researchincludes two aspects: (1) The sister cross population derived from maize GMS materialswere used for sterility analysis and cytological observation. Intact anther observation,isolated cells observation and paraff'm slice were adopted in cytological observationexperiment. (2) The F2 population derived from male sterile materials were used forsterility analysis and simple sequence repeat (SSR) marker location. Linkage analysis with37 pairs of SSR primers from maize chromosome 3 bin 3.06 to shorten the genetic distancebetween molecular marker and the GMS gene, then established the genetic linkage map ofGMS gene region. The main results concluded as follows:1. Sterility investigation in field showed that each sister cross populations (295 plants)were segregated in sterility. Among them, 127 were totally male fertile and 168 weretotally male sterile. Chi-square analysis showed thatχc²=5.424, which was smaller thanχ²(0.01.1)=6.63. The segregating ratio of male fertile plants to male sterile plants fitted well toa 1:1 Mendelian ratio. Sterility investigation in field showed that each F₂ populations (2002plants) were segregated in sterility. Among them, 1539 were totally male fertile and 463were totally male sterile. Chi-square analysis showed thatχc²=3.647, which was smallerthanχ²(0.01, 1) =6.63. The segregating ratio of male fertile plants to male sterile plants fittedwell to a 3:1 Mendelian ratio. The results in sister cross population and F₂ populationindicated that the male sterile trait was governed by a single homozygous recessive GMSgene.2. The sister cross population derived from male sterile materials were used forcytological observation to understand the process of microspore abortion of GMS mutant induced by space flight in maize. The results showed that pollen abortion occured mostlyin dyad stage of meiosis in GMS mutant. The dyad were degenerated with abnormal shape.The pollen mother cells (PMC) and tapetal cells developed abnormally in a few antherbefore the meiosis. The PMCs began to dissolve and degenerate, some PMCs could notbecome normal dyad cells. Some PMCs entered the tetrad stage, but did not complete thefollowing development. The abnormal behavior of tapetal cells lasted from PMC stage todyad stage and tetrad stage. At late anther developing stage, the tapetal cells became tovacuolated, anther chamber was full of giant tapetum and the microspore degeneratedcompletely. The other phenomenon was that the tapetal cells degenerated early, themicrospore degenerated and disappeared. The result of both two types of abortion was thatthe empty anther lacked of pollen.3. The F₂ population derived from male sterile materials were used for SSR locationto determine the precise location of maize GMS gene induced by space flight. According tothe sterility investigation in field, the randomly selected fertile plants and sterile plantswere used for SSR markers selection. On the basis of previous location by Liu, themolecular markers bnlg197 and umc1012 were used to ensure that the GMS gene was onmaize chromosome 3 bin 3.06. At the same time, 37 pairs of of the SSR markers frommaize chromosome 3 bin 3.06 were obtained, and then began to identify SSR markers.Linkage analysis showed that the SSR markers umc1674, umc2076, umc1644, dupssr17,bnlg197, umc2271, umc1951 and bnlg1047 were linked with the GMS gene. Finally theGMS gene was mapped between markers umc2076 and umc1674, with genetic distancesof 4.4 cM and 3.7 cM respectively, then established the genetic linkage map of GMS generegion. This result may benefit for further cloning of this GMS gene.