Identification of salt-tolerance QTL in rice(Oryza sativa L.)

Quantitative trait loci (QTLs) controlling salt-tolerance at the seedling stage in rice (Oryza sativa L.) were identified by interval mapping (SIM) and composite interval mapping (CIM) using a doubled haploid population ZJDH and its high resolution genetic linkage map. The population was derived from an inter-subspecific cross between an indica variety Zhaiyeqing8 (ZYQ8) and a japonica variety Jingxi17 (JX17). Analysis of survival days of seedlings treated with 0.7% NaCl revealed that a major salt-tolerance quantitative trait locus (QTL), Std, was present between markers RG612 and C131 on chromosome 1 when using both MAPMAKER/QTL 1.1 and PLABQTL 1.0 (SIM).Its allele which contributes to salt-tolerance was from ZYQ8. In addition, seven more QTLs which give additive effect on salt-tolerance are identified when using PLABQTL(CIM), and most of them were from JX17.

Molecular cloning, chromosomal mapping and expression analysis of disease resistance gene homologues in rice(Oryza sativa L.)

Resistance-like sequences have been amplified from first strand cDNA and genomic DNA of rice by PCR using oligonucleotide primers designed from sequence motifs conserved between resistance genes of tobacco and Arabidopsis thaliana. 3 PCR clones, designated Osr1, Osr2 and Osr3 which were 98% identical in nucleotide sequence level, have been found to be significantly homologous to known plant resistance genes and all contained the conserved motifs of NBS-LRR type resistance genes, such as P-loop, kinase2a, kinase3a and transmembrane domain. Southern hybridization revealed that rice resistance gene homologues were organized as a cluster in the genome. RFLP mapping using a DH population derived from an indica/japonica cross (Zhaiyeqing 8/Jingxi 17) and an RFLP linkage map assigned two copies of Osr1 and one copy of Osr3 to the distal position of chromosome 12 where a blast resistance QTL has been mapped previously. Northern blot analysis showed that Osr1 gene was constitutively transcribed in rice leaves,

A novel tobacco gene coding for a product similar to bacterial two-component regulators

The two-component signaling system has been studied in bacteria. It takes part in signal transduction of adaptive behavior. Recent studies have shown that a similar two-component system is also present in eukaryotes. Examples of this are ETR1 and CKI1 genes which may involve the signal transduction of plant hormone ethylene and cytokinin respectively. The cloning and characterization of a novel gene ( NTHK1 ) fragment from tobacco are presented.Its partial sequence codes for a product which shows similarity to many two-component signaling proteins. Southern blot analysis indicated that there are 2 to 3 copies of NTHK1 gene in tobacco genome (allotetraploid). Homologous genes may also exist in other plants such as Arabidopsis, soybean and spinach. The expression of NTHK1 gene has also been analyzed in tobacco.Further studies on the isolation of full-length cDNA of NTHK1 gene will elucidate more clearly its function in signal perception and transduction.

Exploration of presence/absence variation and corresponding polymorphic markers in soybean genome

This study was designed to reveal the genome‐wide distribution of presence/absence variation（PAV） and to establish a database of polymorphic PAV markers in soybean. The 33 soybean whole‐genome sequences were compared to each other with that of Williams 82 as a reference genome. A total of 33,127 PAVs were detected and 28,912 PAV markers with their primer sequences were designed as the database NJAUSoyPAV_1.0. The PAVs scattered on whole genome while only 518（1.8%） overlapped with simple sequence repeats（SSRs） in BARCSOYSSR_1.0database. In a random sample of 800 PAVs, 713（89.13%） showed polymorphism among the 12 differential genotypes. Using 126 PAVs and 108 SSRs to test a Chinese soybean germplasm collection composed of 828 Glycine soja Sieb. et Zucc. and Glycine max（L.） Merr. accessions, the per locus allele number and its variation appeared less in PAVs than in SSRs. The distinctness among alleles/bands of PCR（polymerase chain reaction） products showed better in PAVs than in SSRs, potential in accurate marker‐assisted allele selection. The association mapping results showed SSR t PAV was more powerful than any single marker systems.The NJAUSoyPAV_1.0 database has enriched the source of PCR markers, and may fit the materials with a range of per locus allele numbers, if jointly used with SSR markers.

A cryptic inhibitor of cytokinin phosphorelay controls rice grain size

Plant hormone cytokinin signals through histidine-aspartic acid(H-D)phosphorelay to regulate plant growth and development.While it is well known that the phosphorelay involves histidine kinases,histidine phosphotransfer proteins(HPs),and response regulators(RRs),how this process is regulated by external components remains unknown.Here we demonstrate that protein phosphatase with kelch-like domains(PPKL1),known as a signaling component of steroid hormone brassinosteroid,is actually a cryptic inhibitor of cytokinin phosphorelay in rice(Oryza sativa).Mutation at a specific amino acid D364 of PPKL1 activates cytokinin response and thus enlarges grain size in a semi-dominant mutant named s48.Overexpression of PPKL1 containing D364,either with the deletion of the phosphatase domain or not,rescues the s48 mutant phenotype.PPKL1 interacts with OsAHP2,one of authentic HPs,and D364 resides in a region resembling the receiver domain of RRs.Accordingly,PPKL1 can utilize D364 to suppress OsAHP2-to-RR phosphorelay,whereas mutation of D364 abolishes the effect.This function of PPKL1 is independent of the phosphatase domain that is required for brassinosteroid signaling.Importantly,editing of the D364-residential region produces a diversity of semi-dominant mutations associated with variously increased grain sizes.Further screening of the edited plants enables the identification of two genotypes that confer significantly improved grain yield.Collectively,our study uncovers a noncanonical cytokinin signaling suppressor and provides a robust tool for seed rational design.

Mapping Quantitative Trait Loci Associated with Aluminum Toxin Tolerance in NJRIKY Recombinant Inbred Line Population of Soybean (Glycine max)

To investigate the genetic mechanism of AI-tolerance in soybean, a recombinant inbred line population （RIL） with 184 F2：7：11 lines derived from the cross of Kefen9 No.1×Nannong 1138-2 （AI-tolerant×AI-sensitive） were tested in pot experiment with sand culture medium in net room in Nanjing. Four traits, i.e. plant height, number of leaves, shoot dry weight and root dry weight at seedling stage, were evaluated and used to calculate the average membership index （FAi） as the indicator of AI-tolerance. The composite interval mapping （CIM） under WinQTL Cartographer v. 2.5 detected five QTLs （i.e. qFAi-1, qFAi- 2, qFAi-3, qFAi-4 and qFAi-5）, explaining 5.20%-9.07% of the total phenotypic variation individually. While with the multiple interval mapping （MIM） of the same software, five QTLs （qFAi-1, qFAi.5, qFAi.6, qFAi-7, and qFAi-8） explaining 5.7%-24.60% of the total phenotypic variation individually were mapped. Here qFAi-1 and qFAi-5 were detected by both CIM and MIM with the locations in a same flanking marker region, GMKF046-GMKF080 on B1 and satt278-sat_95 on L, respectively. While qFAi-2 under CIM and qFAi-6 under MIM both on Dlb2 were located in neighboring regions with their confidence intervals overlapped and might be the same locus. Segregation analysis under major gene plus polygene inheritance model showed that AI-tolerance was controlled by two major genes （h^2mg=33.05%） plus polygenes （h^2pg=52.73%）. Both QTL mapping and segregation analysis confirmed two QTLs responsible for AI-tolerance with relatively low heritability, and there might be a third QTL, confounded with the polygenes in segregation analysis.

Isolation and characterization of soybean NBS analogs

Isolation of plant resistance genes is greatly helpful to crop resistance breeding and the insight of resistance mechanism. The cloned plant resistance genes are classified into four classes according to their putative structural domain, of which the majority possesses nucleotide-binding site (NBS) domain that consists of P-loop, kinase2a and kinase3a. The conservation of this domain affords the potential possibility of cloning the plant resistance genes, which is homology-based cloning technique. In the present study, the degenerate oligonucleotide primers were designed according to the tobacco N and Arabidopsis RPS2, and 358 clones were isolated from the genomic DNA of resistance soybean culti-var Kefengl, resistant to soybean mosaic virus, and 4 open-reading NBS analogs were finally characterized and designated as KNBS1, KNBS2, KNBS3 and KNBS4. Southern hybridization suggested that they were present with multicopy in the soybean genome; KNBS4 was mapped to F linkage group and KNBS2 co-located J

Molecular markers linked to Rsa resistant to soybean mosaic virus

Soybean mosaic virus （SMV） is a severe disease in worldwide soybean production. A cross was made between Kefeng No.1 with broad spectrum resistance to SMV and Nannong 1138-2, a susceptible cultivar. The inheritance of resistance to SMV strain Sa prevailing in southern China was analyzed. Results of x2 test from inoculation experiment on parents F1, F2 and F3 lines showed that the resistance to strain Sa was controlled by a single dominant gene Rsa. BSA method was adopted and 900 random 10-mer primers were used to amplify total DNA from resistant pool and susceptible pool in order to obtain polymorphic bands in two bulks.16 primers could generate polymorphic bands, of which OPW-05 and OPAS-06 could generate the most stable RAPD patterns. RAPD markers OPW-05660 and OPAS-061800 were found to be linked to Rsa.Their order and genetic distance were OPAS-06（1800）22.2 cM Rsa 10.1 cM OPW-05660. Southern blotting showed that both OPAS-061800 and OPW-05660 were low copy DNA in genomic DNA. OPW-05(

Tobacco floral homeotic gene homologues: partial sequence and expression pattern

Using PCR approach, three cDNA sequences, NTSQUA4, NTSQUA12 and NTSQUA15, were amplified from first_strand cDNAs of wild tobacco flower buds and identified as homologues for floral homeotic genes. All the three clones contained domains that a floral homeotic gene generally had, i.e. I domain, K domain and C_terminal domain except MADS_ box since the PCR primers were designed beyond this region. In addition, the amino acid sequences of them showed 50%-60% identity (70%-80% similarity) with the known floral organ identity class A gene AP1 and SQUA, possibly indicating that they are class A_like genes. NTSQUA4 and NTSQUA412 shared 95% identity in their amino acid sequence, while NTSQUA415 exhibited only 47% identity as compared with NTSQUA4 and NTSQUA12. Within tobacco flower, NTSQUA4 was expressed in sepals, petals and carpels, but not in stamens, while NTSQUA15 was expressed in every whorl of the flower. The possible functions of these genes are discussed.