Ideal type 1 is caused by a point mutation in the a-tubulin gene that affects microtubule arrangement in soybean

Plant architecture is a target of crop improvement.The soybean mutant ideal type 1(it1)displays a pleiotropic phenotype characterized by compact plant architecture,reduced plant height,shortened petioles,wrinkled leaves,and indented seeds.Genetic analysis revealed that the pleiotropic phenotype was controlled by an incomplete dominant gene.We characterized the cellular phenotypes of it1 and positionally cloned the it1 locus.Detailed morphogenetic analysis of the it1 mutant revealed an excess of xylem cells and expanded phloem,and polygonal pavement cells.Positional cloning showed that the phenotype was caused by a G-to-A mutation in the second exon of the a-tubulin gene(Glyma.05G157300).The mutation altered microtubule arrangement in pavement cells,changing their morphology.Overexpression of Gmit1 resulted in an it1-like phenotype and polygonal pavement cells and microtubules of overexpressors were parallel or slightly inclined.Five suppressor mutants able to suppress the phenotype of it1 were obtained by EMS mutagenesis in the it1 background.All these mutants carried an additional mutation in the it1 gene.These results suggest that the pleiotropic phenotype of it1 is caused by the mutation in the atubulin gene.

Map-based cloning of a novel QTL qBN-1 influencing branch number in soybean[Glycine max(L.)Merr.]

Branch number(BN)is an important agronomic attribute related to the plant architecture,adaptability,and yield of soybean.To date,few studies ofBNhave been conducted to elucidate its genetic background.We aimed to localize genetic factors affecting BN using segregating populations derived fromthe high-branching cultivar‘Kennong24’(KN24)and the low-branching cultivar‘Kenfeng19’(KF19).Composite interval mapping analysis detected a QTL(qBN-1)on chromosome 6 between the SSR markers BARCSOYSSR_06_0993 and BARCSOYSSR_06_1070 using an F2 population.To fine-map qBN-1,a RIL population was developed and genotyped with 14 SSRmarkers located in the QTL region.qBN-1 was localized to a 115.67-kb interval flanked by markers BARCSOYSSR_06_1048 and BARCSOYSSR_06_1053.The QTL was further confirmed using backcross populations of size 1305(BC2F2 with KN24 as a recurrent parent)and 1712(BC3F2 with KF19 as a recurrent parent).The fine-mapping region of qBN-1 contained only two candidate genes,Glyma.06G208800 and Glyma.06G208900,whose expression patterns were investigated by qRT-PCR.Compared to Glyma.06G208800 gene expression,Glyma.06G208900 showed the highest expression of the two genes and showed a significant difference in expression between high-and low-branching genotypes in either axillary meristem or shoot apical meristem,and showed opposite expression patterns in the two tissues at V4 and R1 stages.These results identify Glyma.06G208900 as a novel candidate gene controlling BN.Taken together,the results of this study provide a foundation for cloning and functional analysis of the qBN-1 gene and for the improvement of BN bymarker-assisted selection in soybean breeding.