Agrobacterium rhizogenes-dependent production of transformed roots from foliar explants of pepper (Capsicum annuum): a new and efficient tool for functional analysis of genes.

Pepper is known to be a recalcitrant species to genetic transformation via Agrobacterium tumefaciens. A. rhizogenes-mediated transformation offers an alternative and rapid possibility to study gene functions in roots. In our study, we developed a new and efficient system for A. rhizogenes transformation of the cultivated species Capsicum annuum. Hypocotyls and foliar organs (true leaves and cotyledons) of Yolo Wonder (YW) and Criollo de Morelos 334 (CM334) pepper cultivars were inoculated with the two constructs pBIN-gus and pHKN29-gfp of A. rhizogenes strain A4RS. Foliar explants of both pepper genotypes infected by A4RS-pBIN-gus or A4RS-pHKN29-gfp produced transformed roots. Optimal results were obtained using the combination of the foliar explants with A4RS-pHKN29-gfp. 20.5% of YW foliar explants and 14.6% of CM334 foliar explants inoculated with A4RS-pHKN29-gfp produced at least one root expressing uniform green fluorescent protein. We confirmed by polymerase chain reaction the presence of the rolB and gfp genes in the co-transformed roots ensuring that they integrated both the T-DNA from the Ri plasmid and the reporter gene. We also demonstrated that co-transformed roots of YW and CM334 displayed the same resistance response to Phytophthora capsici than the corresponding untransformed roots. Our novel procedure to produce C. annuum hairy roots will thus support the functional analysis of potential resistance genes involved in pepper P. capsici interaction.

Characterization of genetic components involved in durable resistance to stripe rust in the bread wheat 'Renan'.

Stripe rust, caused by Puccinia striiformis f. tritici, is one of the most widespread and destructive wheat diseases in areas where cool temperatures prevail. The wheat cv. Renan, carrying the specific gene Yr17, has shown effective resistance for a long time, even though some pathotypes overcame the Yr17 gene. The objectives of this study were to locate and map genetic loci associated with adult-plant resistance (APR) to stripe rust in a recombinant inbred line population derived from a cross between Renan (resistant) and Récital (susceptible). Field assays were performed for 4 years (1995, 1996, 2005, and 2006) to score disease-progress data and identify APR quantitative trait loci (QTLs). Three QTLs, QYr.inra-2BS, QYr.inra-3BS, and QYr.inra-6B, with resistance alleles derived from Renan were detected in 1995 to 1996 with the 237E141 pathotype, which is avirulent against genotypes carrying Yr17. These QTLs were stable and explained a major part of the phenotypic variation seen in 2005 to 2006, when the 237E141 V17 pathotype was used. Each of these QTLs contributed approximately 4 to 15% of the phenotypic variance and was effective at different adult plant stages. Interactions were observed between some markers of the Yr17 gene and three Renan QTLs: QYr.inra-2BS, QYr.inra-3BS, and QYr.inra-6B. Resistance based on the combination of different APR types should provide durable resistance to P. striiformis.

Genetic analysis of durable resistance to yellow rust in bread wheat.

Yellow rust, caused by Puccinia striiformis, is one of the most damaging diseases affecting bread wheat in temperate regions. Although resistance to yellow rust is frequently overcome by new virulent races, a durable form of resistance in the French bread wheat Camp Remy (CR) has remained effective since its introduction in 1980. We used 217 F7 recombinant inbred lines (RILs) derived from the cross between CR and the susceptible cultivar Recital to identify and map quantitative trait loci (QTLs) involved in durable yellow rust resistance. Six significant QTLs that were stable over a 4-year period were detected. Two QTLs, denoted QYr.inra-2DS and QYr.inra-5BL.2, were located on the short arm of chromosome 2D and the long arm of chromosome 5B, respectively. Each explained on average 25-35% of the observed phenotypic variation and were probably inherited from Cappelle Desprez, a parent of CR that confers durable adult plant resistance to yellow rust. QYr.inra-2DS probably corresponds to the Yr16 gene. The most consistent QTL, designated QYr.inra-2BL, was located on the centromeric region of chromosome 2B and explained 61% of the phenotypic variation in 2003. This QTL was responsible for seedling-stage resistance and may correspond to a cluster of genes, including Yr7. The remaining QTLs were mapped to the short arm of chromosome 2B (R2=22-70%) and to the long arm of chromosomes 2A (R2=0.20-0.40) and 5B (R2=0.18-0.26). This specific combination of seedling and adult plant resistance genes found in CR and CD may constitute the key to their durable resistance against yellow rust.

Homoharringtonine and low-dose cytarabine in the management of late chronic-phase chronic myelogenous leukemia.

PURPOSE: : To evaluate the efficacy and toxicity profiles of a combination regimen of homoharringtonine (HHT) and low-dose cytarabine (ara-C) in patients with Philadelphia chromosome (Ph)-positive chronic myelogenous leukemia (CML) who had experienced treatment failure with interferon alfa (IFNalpha) therapy. PATIENTS AND METHODS: One hundred five patients were treated: 100 in chronic phase (15 with cytogenetic clonal evolution) and five in accelerated phase. Their median age was 52 years; all had been treated unsuccessfully with IFNalpha; 94% were in late chronic phase; 43% had been exposed to ara-C and 11% had been exposed to HHT. Patients received HHT 2.5 mg/m(2) by continuous infusion daily for 5 days and ara-C 15mg/m(2) daily in two subcutaneous injections for 5 days every 4 weeks. The outcome of the 100 patients in chronic phase was compared with a previous study group of 73 patients treated with HHT alone. RESULTS: Overall, the complete hematologic response (CHR) rate in chronic phase was 72%; the cytogenetic response rate was 32% (major response, 15%; complete response, 5%). Toxicities were acceptable, mostly related to moderate diarrhea (3%), headaches (3%), cardiovascular events (3%),and myelosuppression-associated complications (3% to 14%). With a median follow-up period of 25 months, the estimated 4-year survival rate was 55%. Response rates were identical with HHT plus ara-C versus HHT alone, but the survival was significantly longer with the combination after accounting for differences in the study groups and by multivariate analysis. CONCLUSION: The combination regimen of HHT and ara-C is effective and safe in patients with CML who have experienced treatment failure with IFNalpha and needs to be investigated together with IFNalpha as part of front-line CML therapy. The addition of ara-C did not improve the response rates but may have improved survival, perhaps through suppression of clones related to disease transformation.