Mapping QTL associated with resistance to Fusarium head blight in the Nanda2419 x Wangshuibai population. II: type I resistance.

Fusarium head blight (FHB) is a serious disease in wheat and barley affecting both yield and quality. To identify genes for resistance to infection, the RIL population derived from 'Nanda2419' x 'Wangshuibai' and the parents were evaluated for percentage of infected spikes (PIS) in four different environments. Using a 2,960 cM marker framework map constructed for this population, ten chromosome regions were detected for their association with type I resistance through interval mapping with Mapmaker/QTL, among which QTLs mapped in the intervals of Xwmc349--Xgwm149 on chromosome 4B, of Xwmc96--Xgwm304 on chromosome 5A and of Xgwm408--Xbarc140 on chromosome 5B were revealed in at least three environments and have Wangshuibai as the source of resistance alleles. Qfhi.nau-4B and Qfhi.nau-5A had larger effects and explained up to 17.5 and 27.0% of the phenotypic variance, respectively. To detect epistasis QTLs, two-locus interactions were examined by whole genome scan. Interactions of five locus pairs were found to have significant effects on type I resistance with the LOD score ranging 3.8-6.5 and four of them conferred resistance in parental phase. The one with the most significant effect was Xcfd42--Xgwm469 (6D)/Xwmc390-2--Xbd04 (2A) pair. No QTL x E interaction was detected for PIS. It was found that flowering time did not have significant effects on PIS in this population. Our studies indicated that Wangshuibai is useful for breeding for both type I and type II scab resistance and the markers associated with the QTLs could be used in marker-assisted selection and isolation of scab-resistance QTLs.

Mapping QTL associated with resistance to Fusarium head blight in the Nanda2419 x Wangshuibai population. I. Type II resistance.

Scab disease caused by Fusarium spp. has been a major concern for both wheat producers and consumers. Deployment of scab-resistant varieties is the major strategy to curb this disease. To identify the scab resistance genes in wheat cv. Wangshuibai, we produced a F(6:7) recombinant inbred line (RIL) population by crossing Wangshuibai with the scab-susceptible cultivar Nanda2419. The RILs were evaluated for scab resistance in the field by single floret inoculation in two replicates in 2002 and one replicate in 2003. The number of diseased spikelets (NDS) and the length of diseased rachides (LDR) were investigated to reflect the Type II resistance. Among 654 simple sequence repeat (SSR) markers surveyed, 326 were found to be polymorphic between the parents. A partial molecular map was constructed with these markers that covered over 2,210 cM of the wheat genome. Six chromosome regions showed association with both NDS and LDR in a one-way anova analysis, even though the variation explained by them varied between the two traits. Eight intervals were detected for their association with Type II resistance through interval mapping, five of which were not identified in single-point analysis. The quantitative trait loci (QTL) with large effects were the ones in the interval of Xgwm533-3-Xgwm533-1 on chromosome 3B and in the interval of Xwmc539-Xbarc024 on chromosome 6B, whose alleles favoring resistance originate from Wangshuibai. In addition, a QTL whose resistance allele originated from Nanda2419 was consistently detected in the interval of Xs1021m-Xgwm47-1 on chromosome 2B. These results suggest that Wangshuibai is the major source for Type II resistance in this population. The markers associated with these QTL would facilitate the use of scab-resistant genes of Wangshuibai in scab resistance breeding programs of wheat.

PCR-based markers for the powdery mildew resistance gene Pm4a in wheat.

Gene tagging is the basis of marker-assisted selection and map-based cloning. To develop PCR-based markers for Pm4a, a dominant powdery mildew resistance gene of wheat, we surveyed 46 group 2 microsatellite markers between Pm4a near-isogenic line (NIL) CI 14124 and the recurrent parent Chancellor (Cc). One of the markers, gwm356, detected polymorphism and was used for genotyping an F(2) population of 85 plants derived from CI 14124 x Cc. Linkage mapping indicated that Xgwm356 was linked to Pm4a at a distance of 4.8 cM. To identify more PCR-based markers for Pm4a, we also converted the restriction fragment length polymorphism marker BCD1231 linked to it into a sequence-tagged site (STS) marker. The STS primer designed based on the end sequences of BCD1231 amplified an approximately 1.6-kb monomorphic band in both parents. Following digestion of the products with the four-cutter enzymes HaeIII and MspI, it was discovered that the band from CI 14124 consisted of at least two products, one of which had a digestion pattern different from the band from Cc. In the F(2) population, the cleaved polymorphism revealed by the STS marker between the parents co-segregated with powdery mildew resistance. To design Pm4a-specific PCR markers, the 1.6-kb band from Cc and the fragment associated with Pm4a in CI 14124 were sequenced and compared. Based on these sequences a new PCR marker was identified, which detected a 470-bp product only in the Pm4a-containing lines. These PCR-based markers provide a cost-saving option for marker-assisted selection of Pm4a.

[Substance P depresses GABA-activated currents in cultured hippocampal pyramidal neurons of rats].

The purpose of the present study was to explore whether substance P (SP) modulates the response mediated by GABAA receptors. Experiments were carried out on cultured hippocampal pyramidal neurons of rats. GABA-activated inward currents were recorded using the whole-cell-patch-clamp technique. The majority of the neurons examined (66/92, 72%) were sensitive to both GABA and SP. When the neurons were treated with SP prior to application of GABA, the GABA-activated current (IGABA) was inhibited markedly, which was concentration-dependent and could be blocked by spantide, an NK1 receptor antagonist. With 10(-8), 10(-7), 10(-6) and 10(-5) mol/L SP, IGABA was inhibited by 18%, 24.8%, 25.9% and 28% respectively. Intracellular application of H7, a potent inhibitor of PKC, abolished inhibition of IGABA by SP, suggesting that the inhibition of IGABA by SP may be a result of intracellular phosphorylation of the GABAA receptor.

[Current responses mediated by endogenous GABA(B) and GABA(C) receptors in Xenopus oocytes].

The properties of GABA-activated current in Xenopus oocytes and its underlying mechanism were studied using the two-electrode voltage-clamp technique. External application of GABA (10(-10) - 10(-3)mol/L) induced a concentration-dependent outward current in a proportion of oocytes (35.5%, 55/155). Selective GABA(A) receptor antagonist bicuculline (10(-5) mol/L) did not block the GABA-activated current (n=6). However, 2-hydroxysaclofen (10(-4) mol/L), a GABA(B) receptor antagonist, reversed the GABA-activated outward current to an inward current (n=9), which was abolished completely by application of I4AA (10(-5) mol/L), a GABA(C) receptor selective antagonist (n=6). In 20% (12/60) of oocytes, application of baclofen (10(-10) - 10(-4) mol/L), a GABA(B) receptor agonist, also induced a concentration-dependent outward current 2-Hydroxysaclofen at the concentrations of 3 x 10(-6), 3 x 10(-5) and 3 x 10(-4) mol/L blocked the baclofen(10(-5) mol/L)-activated outward current by (6.3+/-3.2) %, (44.1+/-2.2) %, and (86.0+/-1.6) %, respectively (n=6). The reversal potential for baclofen-activated current was around 96.8+/-7.2 mV (n=6), and the baclofen-activated current could be blocked by TEA (n=5) and Ba(2+) (n=5). These results suggest that there exist endogenous GABA receptors, GABA(B) receptors mediating a slow and sustained outward current and GABA(C) receptors mediating an inward current in follicular Xenopus oocytes.

[Modulation of GABA-activated currents by oxytocin in rat dorsal root ganglion neurons].

Experiments were performed on freshly isolated dorsal root ganglion (DRG) neurons of rat. GABA(A)-activated currents were recorded using the whole-cell patch clamp technique. The majority of the neurons (48/52, 90.5%) were sensitive to GABA (10( 6)~10( 3) mol/L). Application of oxytocin (OT) induced outward membrane responses in 51.3% (20/39) of the neurons, no apparent responses in 43.6% (17/39) and inward responses in 5.1% (2/39). 10( 12), 10( 11), 10( 10) and 10( 9) mol/L OT increased 10( 4) mol/L GABA-activated currents to 24.1+/-7.6% (n=6), 33.4+/-6.9% (n=9), 40.2+/-6.5% (n=13) and 67.2+/-14.8% (n=5), respectively. After preapplication of OT, the Kd value for GABA(A)-activated currents decreased, while the response obtained at the maximum concentration increased. The results suggest that the enhancement of GABA-activated currents by OT may suppress primary sensory transmission by potentiating pre-synaptic inhibition of GABA.

Responses of serotonergic and non-serotonergic neurons in the rat nucleus raphe magnus to systemic lysergic acid diethylamide.

Serotonergic and non-serotonergic neurons in the nucleus raphe magnus were identified by conduction velocities and spontaneous discharge rates. Eight of 13 serotonergic neurons were depressed by lysergic acid diethylamide (LSD) administration (40-50 micrograms/kg, i.p. or i.v.), while the others were non-responsive. Among 38 non-serotonergic neurons, 5 were depressed, 4 were excited and 29 were unaffected by systemic LSD at the same doses. It is thus concluded that LSD could act differently on serotonergic and non-serotonergic neurons in nucleus raphe magnus.