Genetic Analysis And Gene Mapping Of Dwarf Mutant Sil And Green-revertible Albino Mutant Wtg Induced By Space Environment In Maize

Space mutation breeding was a comprehensive technologies contained space technology,traditional genetic breeding technology and molecular biology technology.It is a new kind of interdisciplinary breeding technology.Space mutation has been a new kind of artificial mutagenesis in decades.The Maize Research Institute of Sichuan Agricultural University used the return aerial satellite "Practice No.8" to carry the fine backbone inbred lines 18-599,08-641,RP125 and so on into space in 2006.Our research group found a dwarf mutant named sil tentatively and a green-revertible albino mutant named wtg tentatively from these mutagenesis materials.Agronomic traits,genetic traits and preliminary gene mapping were researched in this study.The main research results are as follows:1.The plant height and ear height of the dwarf mutant sil were about 100 cm and 20 cm respectively.For the sil,the number of internodes was constant and the length of each internode was extremely significantly shortened.The internodes below the female ear of sil were shortened more obviously.The leaf of the dwarf mutant sil clustered on the stems,the shape of the leaf shorter and wider.the leaf colour is dark green.The flowering period was prolonged by 3 to 4 days,and the grain yield of single spike was slightly decreased but the difference was not significant in the dwarf mutant sil.The lengthways length of the internodal cells was shortened distinctly and the cross section of the internodal cells did not change significantly in the dwarf mutant sil.Dwarf mutant sil can respond to exogenous Gibberellin GA3 showing increased plant height,but can not restore to wild type,slightly responded to exogenous Auxin IAA,barely responsed to exogenous Brassinosteroids BL.2.The plant height of(B73×sil)F1,(sil×huang zao si)F1 is higher than their respective parents.At the same time,the above two F1 crosses were self-pollenated to form their F2 populations.The segregation ratios of dwarf mutant plants and normal plants in the two F2 populations all fit to 3:1 via chi-square test.The above results suggested that the dwarf mutant sil was controlled by one recessive nuclear gene.We further mapped the sil gene in the(B73×sil)F2 population utilized 317 SSR molecular markers which well-distributed on 10 maize chromosomes from maizeGDB and 34 InDel molecular markers using the molecular marker gene mappping technology based on bulked segregation analysis(BSA).Finally,the target gene sil was mapped between SSR markers umc2396 and SSR marker umc 1147 on the long arm of maize chromosome 1 with genetic distances of 0.36 cM and 10.2 cM respectively.We obtained InDel marker A4 closely linked to the target gene sil.3.For the albino mutant wtg,from sprouting to two leaves stage,the leaves were albino,and then gradually turn green.The leaves of the albino mutant wtg almost completely turn green at the 40th days after sowing,but the leaf color change of wtg is affected by temperature alter,illumination changes and so on.The plant height and panicle height of the albino mutant wtg increased significantly,and the grain yield per ear slightly decreased,but the difference was not significant.Before the leaves turn green,the contents of the chlorophyll a,chlorophyll b and carotenoid of albino mutant wtg were 6.34%,2.87%,16.47%compared with those in normal sublines nor in the same generation.Meanwhile,pathological changes of diseased chloroplasts’morpholo-gy and structure took place and the mutant wtg lacked thylakoid slice layer and granas,only had plenty of small vesicle-like structures in the chloroplasts.As the leaves turn green,photosynthetic pigment content gradually increased,the chloroplast internal structure gradually restored.After the leaves turn green,the contents of the chlorophyll a,chlorophyll b and carotenoid of wtg were 81.73%,58.26%,63.63%,compared with those in normal sublines nor in the same generation.Meanwhile complete chloroplast membrane system structure and distinct thylakoid grana slice layer structure,tidy and compact thylakoids appared in the albino mutant wtg,and the overall structure of the chloroplast of the albino mutant wtg is basically identical as normal chloroplast.4.Three F1 crosses included(B73×wtg)F1,(wtg×huang zao si)F1 and(Mol7×wtg)F1 all showed normal green leaves.At the same time,the above three F1 crosses were self-pollenated to form their F2 populations.The segregation ratios of green leaf plants and albino mutant plants in the three F2 populations all fit to 3:1 via chi-square test.The above results suggested that the mutant wtg was controlled by one recessive nuclear gene.We further mapped the wtg gene in the(B73×wtg)F2 population utilized 320 SSR molecular markers in maizeGDB and 24 InDel molecular markers using the molecular marker gene localization technology based on BSA analysis.Finally,the target gene wtg was mapped between InDel markers HY4BH-12 and SSR marker umc2176 on the short arm of maize chromosome 4 with genetic distances of 0.85 cM and 0.85 cM respectively with a physical interval of 340 kb.We obtained SSR marker umc2281 closely linked to the target gene wtg.