Enhanced Stem Nematode Resistance of Transgenic Sweetpotato Plants Expressing Oryzacystatin-I Gene

Enhanced stem nematode resistance of transgenic sweetpotato （cv. Lizixiang） was achieved using Oryzacystatin-I （OCI） gene with Agrobacterium tumefaciens-mediated transformation. A. tumefaciens strain EHA105 harbors a binary vector pCAMBIA1301 with OCI gene, gusA gene and hptII gene. Selection culture was conducted using 25 mg L-1 hygromycin. A total of 1 715 plants were produced from the inoculated 1 450 cell aggregates of Lizixiang via somatic embryogenesis. GUS assay and PCR analysis of the putative transgenic plants randomly sampled showed that 90.54% of them were transgenic plants. Transgenic plants exhibited significantly enhanced resistance to stem nematodes compared to the untransformed control plants by the field evaluation with stem nematodes. Stable integration of the OCI gene into the genome of resistant transgenic plants was confirmed by Southern blot analysis, and the copy number of integrated OCI gene ranged from 1 to 4. Transgene overexpression in stem nematode-resistant plants was demonstrated by quantitative real-time PCR analysis. This study provides a way for improving stem nematode resistance in sweetpotato.

Marker Assisted Selection in Citrus Rootstock Breeding Based on a Major Gene Locus ‘Tyr1’Controlling Citrus Nematode Resistance

Based on the former constructed ＇Tyrl＇ locus genetic map in family 9145, from LB6-2 [Clementine mandarin （C. reticulata） × Hamlin orange （C. sinensis）] × Swingle citrumelo （C. paradise × P. trifoliata）, 9 markers were chosen for application in evaluating their effectiveness in marker-assisted selection （MAS） for citrus rootstock breeding program from many F1 progeny of Poncirus trifoliata. As the mapping revealed that these markers were estimated within a range of 12.1 cM in the linkage group, and among them, SCO07 co-segregated with ＂Tyrl＇, and 7A4R as the closest to ＇Tyrl＇ with a distance of 1.5 cM, these markers were basically fitful to go MAS screening. The results of screening P. trifoliata F1 progeny indicated that all the markers were inherited in codominant fashion and most of them were heterozygous on PT （Pomery of P. trifoliata）., marker 4L17R/CfoI and 7A4（1407）/BfaI were proved to be consistently reliable for accurate scoring of genotypes and the revealed polymorphism was basically coincided with the citrus nematode resistant phenotype within tested populations. The polymorphic genotype with marker 4L17R/Cfol was found completely matched up with the phenotype of individuals that conferred high resistance to citrus nematode when the USDA hybrid rootstocks were screened. Utilization of these markers, especially the highly specific 4L17R/Cfol and 7A4（1407）/Bfal, should result in great benefit to world citrus industry for early selection in rootstock-breeding program.

Breeding Soybeans for Resistance to Physiological Race 4 of Cyst Nematode

Soybean cyst nematode causes serious damage to soybean production. In 1991, we started breeding studies on the resistance of soybeans to the cyst nematode. We found that near the Beijing area the dominant race of the cyst nematode was race 4. We made more than 50 combinations of cross. The best combination was Dan 8 X PI 437654 which resulted in marked segregation in plant height, pod habit, resistance to cyst nematode and maturity. We obtained many new soybean lines highly resistant to the cyst nematode through the pedigree method of selection, enlarging the number of plants of good combinations, alternative breeding in the North and in the South, and identification at an early generation. We now have released three soybean cultivars, Zhonghuang 12, Zhonghuang 13 and Zhonghuang 17 with moderate resistance to the cyst nematode in Beijing, Anhui, Tianjin and Northern China. In addition, we obtained many lines which were highly resistant to the cyst nematode.

Missense mutation of a class B heat shock factor is responsible for the tomato bushy root-2 phenotype

The bushy root-2(brt-2)tomato mutant has twisting roots,and slower plant development.Here we used whole genome resequencing and genetic mapping to show that brt-2 is caused by a serine to cysteine(S75C)substitution in the DNA binding domain(DBD)of a heat shock factor class B(HsfB)encoded by SolycHsfB4a.This gene is orthologous to the Arabidopsis SCHIZORIZA gene,also known as AtHsfB4.The brt-2 phenotype is very similar to Arabidopsis lines in which the function of AtHsfB4 is altered:a proliferation of lateral root cap and root meristematic tissues,and a tendency for lateral root cap cells to easily separate.The brt-2 S75C mutation is unusual because all other reported amino acid substitutions in the highly conserved DBD of eukaryotic heat shock factors are dominant negative mutations,but brt-2 is recessive.We further show through reciprocal grafting that brt-2 exerts its effects predominantly through the root genotype even through BRT-2 is expressed at similar levels in both root and shoot meristems.Since AtHsfB4 is induced by root knot nematodes(RKN),and loss-of-function mutants of this gene are resistant to RKNs,BRT-2 could be a target gene for RKN resistance,an important trait in tomato rootstock breeding.Gene&accession numbers SolycHsfB4a-Solyc04g078770.