Cloning and expression analysis of a stress-induced GmIMT1 gene in soybean (Glycine max).

Here, we aimed to clone and identify the GmIMT1 gene related to the salt stress response in soybean. The full-length cDNA sequence of the GmIMT1 gene was amplified in soybean using degenerate primers of Mesembrythmum crystallium. To understand the stress response, the GmIMT1 gene was cloned and sequenced. Then, the expression vectors of the gene were constructed, and introduced into the model plant Arabidopsis thaliana through Agrobacterium mediated transformation, and the salt tolerance was analyzed in the transgenic plants. In addition, the expression patterns of GmIMT1 gene in soybean were analyzed. The expression was examined in different organs (roots, leaves, flower seeds, and stem) and under different stress conditions (drought, high salt, low temperature, salicylic acid, ethane, abscisic acid, and methyl jasmonate) by real-time fluorescent quantitative polymerase chain reaction analysis. The results showed that the root, leaves, and stems exhibited high level of GmIMT1 gene expression, whereas there was no expression in the seeds. In addition, the GmIMT1 gene expression was upregulated under all stress conditions. Overall, the results clearly indicate that GmIMT1 might be involved in multiple plant response pathways to the different environmental conditions. Furthermore transgenic plants exhibited higher salt-tolerance compared to wild type plants.

Molecular evolution of two consecutive carotenoid cleavage dioxygenase genes in strigolactone biosynthesis in plants.

Strigolactones are newly discovered plant hormones that perform various functions, from signaling in symbiotic interactions with arbuscular mycorrhizal fungi to controlling outgrowth of axillary buds. We examined the phylogenetic relationships of two carotenoid cleavage dioxygenase genes (CCD7 and CCD8) that are involved in consecutive upstream steps of the proposed strigolactone biosynthesis pathway. The CCD7 and CCD8 sequences from 11 model species, divided into two clades, correspond to sequences from monocotyledons and dicotyledons. However, the sequences from the primitive moss, Physcomitrella patens, appeared to be evolutionarily distinct from those of the angiosperms. CCD7 and CCD8 are much conserved, since no significant positive selection was detected among these plants. Ks values indicated that CCD7 and CCD8 diverged about 290 to 430 million years ago. As essential genes in the strigolactone pathway, the divergence timing of the conserved CCD7 and CCD8 genes reflects the approximate time of generation of strigolactone as a regulatory substance. This timing calculation also coincides with initiation of symbiosis between plants and microorganisms, inferred from the fossil record. Molecular evolution analyses of genes in metabolic pathways can provide insight concerning gene evolution.

Identification and Distribution of Soybean mosaic virus Strains in Southern China.

From 1,417 leaf samples with Soybean mosaic virus (SMV)-like symptoms collected from about 1,500 fields of 117 counties of 13 provinces in Southern China during 2004 to 2006, 201 SMV isolates were obtained after biological purification with single-lesion isolation and serological determination. Based on disease reactions on 10 differentials used in China as a representative from various reported differential cultivar systems, the isolates were grouped into 12 strains. Among them, eight were the same as those previously reported from Northeast China and the Huang-Huai Valleys while the other four were new and were designated as SC18, SC19, SC20, and SC21. Strains SC15 and SC18, which were predominant and widespread in Southern China, accounted for 32.3 and 26.4% of the total isolates and were distributed in 9 and 10 provinces, respectively. Thus far, 21 strains have been identified in the three soybean-producing regions in China under the uniform differentials system. According to their responses on the 10 differentials, the strains were clustered into five groups at similarity coefficient 0.6. Among them, SC15 in cluster V is the most virulent strain because it infects all differentials. Therefore, specific attention should be placed on control of its prevalence in soybean production.

[Identification of mixed major genes and polygenes inheritance model of quantitative traits by using DH or RIL population].

The accuracy of the mixed inheritance analysis of quantitative traits with larger experimental error could be improved while using DH or RIL population. The segregation analysis method of identifying mixed major genes and polygenes inheritance model, including linkage inheritance model, of quantitative traits by using DH or RIL population was developed in this paper. The method may be applied to identify the mixed major gene and polygenes inheritance model of quantitative traits, estimate genetic effects and variances of major genes and polygenes, and the recombination value while there is linkage between two major genes. Finally, an example was used to illuminate the above procedure.

[A study of the inheritance and linkage of resistance to four strains of soybean mosaic virus in soybeans].

Ten susceptible x resistant and resistant x resistant crosses were made among eight varieties, of which seven were previously identified as resistant to one to four SMV strains, in order to investigate the inheritance of resistance to the four strains (Sa, Sc, Sg, and Sh) and the linkage relationship among the resistant genes. Seeds from F2 individual plants were randomly divided and planted in two separated nurseries, in which the seedlings were inoculated with two different strains. The genotype of each F2 plant was detected from the reaction of its F3 progenies to the two strains. The results showed that the resistance to each of the four strains was conditioned by a dominant gene which was labelled here with Ra, Rc, Rg, and Rh, respectively. All the four loci appeared to be in a same linkage group with the order of Rg--Rh--Ra--Rc. The recombination value between Ra and Rc was estimated to be 25.4 +/- 7.7%, and those between Rg and Rh, Ra and Rh, Ra and Rg, and Rc and Rg to be 27.3 +/- 5.4%, 23.5 +/- 5.2%, 41.1 +/- 8.5%, and 46.5 +/- 7.5%, respectively. The genes resistance to Sa in Kwanggyo and "7222" were determined at the same locus, so were the resistant genes for Sc. In addition, this linkage group seemed to be not related with the first and eighth linkage group.

[Major gene plus poly-gene inheritance of erucic acid content in Brassica napus L].

Inheritance of erucic acid content in the cross of HSTC14 x Ningyou 7 (Brassica napus L.) was investigated by applying the major gene plus poly-gene model of quantitative traits to a joint analysis of multi-generations (P1, F1, P2, B1:2 B2:2 and F2:3). The results showed that erucic acid content in the cross of HSTC14 x Ningyou 7 was controlled by two major genes with additive-dominance-epistatic effects plus polygenes with additive-dominance effects (the E-1 model). Heritability values of the major genes of B1:2, B2:2 and F2:3 population were estimated as 69.47%, 28.25% and 51.33% respectively, while those of polygene were 29.81%, 70.39% and 47.86%. This results demonstrated that erucic acid content level in the cross was mainly controlled by two major genes mixed with the effect of polygenes. The estimated additive effects of the two major genes, da and db, were -12.1712 and -6.5423 respectively. The dominant effect of the first major gene was 9.1011, much higher than that of the second one. The interaction effect of the first major gene's additive effect and the second major gene's dominance effect was 22.4400, while that between the second major gene's additive effect and the first major gene's dominance effect was only 1.0317. There were obvious differences in genetic effects between the two major genes. The effect of db was only about 53.75% that of da, indicating that the contributions to erucic acid level of the two major genes was not equal in the cross. The possible reasons resulting in the difference was discussed in this paper.

[Major-polygene effect analysis of resistance to bacterial blight (Xanthomonas campestris pv. oryzae) in rice].

Five crosses between resistance and susceptible were analyzed to study major-polygene effect using major-polygene mixed mode. The result showed that 3 of 5 crosses were controlled by both major gene and polygene. In addition, there were large variation of additive effect, variance as well as heredity of major gene polygene in 3 crosses. Major gene was predominant in resistant variation, but durability should be considered. We suggested that construct major-polygene system be constructed in the long run in breeding program to ensure a durable and high level of resistance to constrain fluctuation of races of Xanthomonas campestris pv. oryzae population.

[A study on the inheritance of dried tofu output of soybean].

The P1, P2, F1, F2 and F2:3 in plant generation of three crosses of Liuhexiaoyeqing x Xinyixiaohedou, Shangraoganbusi x Huaiyinqiuhedou and Liuhexiaoyeqing x Nannong 73-935 were used to study the inheritance of dried tofu output. The results of the joint analyses of multiple plant generations showed a consistant one major gene plus polygene mixed inheritance model. The heritability values for dried tofu output were as high as 87.84%-99.98%. In plant generation F2:3 of these crosses, the heritabilities of major gene were 51.80%-61.85%, and those of polygene were 36.12%-48.03%. Therefore, both major gene and polygene effects were important and should be utilized in breeding program.

[Development and expression process of inheritance of resistance to cotton worm (Prodenia litura) in soybeans].

Cotton worm [Prodenia litura(Fabricius)] was one of the major leaf-feeders for soybeans in Southern China. Resistance to leaf-feeders has been recognized as one of the major breeding target traits in the National Soybean Breeding Program. This paper deals with the study of inheritance of resistance of soybeans to cotton worm [Prodenia litura(Fabricius)]. P1, P2, F1, F2, F2:3 of four susceptible x resistant crosses, i.e. N21297 x N1178-2-2, N21266 x N23860, N119-1 x N1178-2-2 and N21266 x N3039, were used in the study. The materials were planted in net room under artificial infestation in 1996-1998. The data of defoliation percentage of successive development stages, during cotton worm damage period were obtained and collected for genetic analysis. The segregation analysis methods for major genes plus polygene mixed inheritance model developed by Gai et al. were used to identify the genetic system of resistance. The results from joint analyses of multiple segregating generations as well as from analyses of single F2 or F2:3 generations of the four crosses showed a two major genes plus polygene mixed inheritance model at fully developed stages of resistance while one or two major genes with or without polygene were observed at other stages. Between the two major genes, the additive effect of one locus was from 1.56 to 9.89(%, defoliation), another from -3.79 to 3.75(%, defoliation). The heritability values of major genes were estimated as 70.40%-99.21%, greater than those of polygene which were only 0.00%-22.29%. Therefore, in the improvement of resistance to cotton worm, major gene resistance should be considered at first.

[Microsatellite marker analysis of a soybean recombinant inbred line NJRIKY].

The prerequisite of genomic research such as genetic mapping is construction of a suitable segregating population and its reasonable evaluation before use. A recombinant inbred line (RILs), NJRIKY, was constructed through a cross between Kefeng 1 and Nannong 1138-2. The present study was focused on evaluation of genetic structure of the RILs through the simple sequence repeats (SSRs) analysis. A total number of 138 pairs of SSRs primers covering the whole soybean genome were randomly selected for polymorphic analysis between two parents. 86 pairs of which were polymorphic and polymorphic rate is up to 62.32%. 90 polymorphic loci were found. Further analysis with polymorphic SSRs loci on the sampled lines indicated that not only segregation of most SSRs loci conformed to the ratio of 1:1, but also almost each sampled line tended to homozyge. The distribution of genotypic composition was normal. The population is ideal for genetic mapping and other genomic research.

[QTLs mapping of some agronomic traits of soybean].

A recombinant inbred population of soybean was developed from a intraspecies cross of Kefeng1 and Nannong 1138-2. A genetic linkage group of soybean genome was constructed, which composed of 22 linkage groups, included 302 loci, covered 2,363.8 cM. The interval mapping was used to identify quantitative trait loci (QLTs) associated with ten important agronomic traits in the RIL population. The results indicated that thirty-four QTLs were detected for the ten traits associated with yield and seed quality. We conclude that QTL analysis offers a useful tool for the genetic improvement of soybean cultivars.

[Construction and analysis of a genetic linkage map of soybean].

A high-density genetic map was constructed with a RILs population (NJRIKY) from a cross of two cultivated soybean Kefeng 1 and Nannong 1138-2, using RFLP, SSR, RAPD and AFLP markers. The map consists of 24 linkage groups, which include 792 genetic markers, and covers 2,320.7 cM with an average genetic distance of 2.9 cM. The higher polymorphsims between two parents were identified with SSR markers. Due to its simplicity and stability, they could be used as anchored marker to integrate different maps constructed with different genetic markers. AFLP marker system is efficient for map construction while it easily form clusters to cause big gaps in the map. A total of 21.7% of markers was found with distorted segregation in the RILs population. The high-density molecular linkage map is fundamental for gene localization, comparative genomics, and QTL mapping of important agronomic traits.

QTL mapping of ten agronomic traits on the soybean ( Glycine max L. Merr.) genetic map and their association with EST markers.

A set of 184 recombinant inbred lines (RILs) derived from soybean vars. Kefeng No.1 x Nannong 1138-2 was used to construct a genetic linkage map. The two parents exhibit contrasting characteristics for most of the traits that were mapped. Using restricted fragment length polymorphisms (RFLPs), simple sequence repeats (SSRs) and expressed sequence tags (ESTs), we mapped 452 markers onto 21 linkage groups and covered 3595.9 cM of the soybean genome. All of the linkage groups except linkage group F were consistent with those of the consensus map of Cregan et al. (1999). Linkage group F was divided into two linkage groups, F1 and F2. The map consisted of 189 RFLPs, 219 SSRs, 40 ESTs, three R gene loci and one phenotype marker. Ten agronomic traits-days to flowering, days to maturity, plant height, number of nodes on main stem, lodging, number of pods per node, protein content, oil content, 100-seed weight, and plot yield-were studied. Using winqtlcart, we detected 63 quantitative trait loci (QTLs) that had LOD>3 for nine of the agronomic traits (only exception being seed oil content) and mapped these on 12 linkage groups. Most of the QTLs were clustered, especially on groups B1 and C2. Some QTLs were mapped to the same loci. This pleiotropism was common for most of the QTLs, and one QTL could influence at most five traits. Seven EST markers were found to be linked closely with or located at the same loci as the QTLs. EST marker GmKF059a, encoding a repressor protein and mapped on group C2, accounted for about 20% of the total variation of days to flowering, plant height, lodging and nodes on the main stem, respectively.