Transposon mutagenesis of pseudomonas syringae pathovars syringae and morsprunorum to identify genes involved in bacterial canker disease of cherry

Bacterial canker of Prunus, affecting economically important stone fruit crops including cherry, peach, apricot and plum, is caused by the plant pathogen Pseudomonas syringae (P.s.). Strains from two pathovars—P.s. pv. syringae (Pss) and P.s. pv. morsprunorum race 1 (PsmR1) and 2 (PsmR2)—in three phylogenetically distant clades have convergently evolved to infect Prunus. The bacteria enter woody tissues through wounds and leaf scars, causing black necrotic cankers. Symptoms are also produced on blossom, fruit and leaves. Little is known about the mechanisms P.s. uses to colonise tree hosts such as Prunus. Here, we created transposon (Tn) mutant libraries in one strain of P.s. from each of the three clades and screened the mutants on immature cherry fruit to look for changes in virulence. Mutants (242) with either reduced or enhanced virulence were detected and further characterised by in vitro screens for biofilm formation, swarming ability, and pathogenicity on leaves and cut shoots. In total, 18 genes affecting virulence were selected, and these were involved in diverse functions including motility, type III secretion, membrane transport, amino acid synthesis, DNA repair and primary metabolism. Interestingly, mutation of the effector gene, hopAU1, led to an increase in virulence of Psm R

Identifying resistance in wild and ornamental cherry towards bacterial canker caused by Pseudomonas syringae

Bacterial canker is a major disease of stone fruits and is a critical limiting factor to sweet cherry (Prunus avium) production worldwide. One important strategy for disease control is the development of resistant varieties. Partial varietal resistance in sweet cherry is discernible using shoot or whole tree inoculations; however, these quantitative differences in resistance are not evident in detached leaf assays. To identify novel sources of resistance to canker, we used a rapid leaf pathogenicity test to screen a range of wild cherry, ornamental Prunus species and sweet cherry × ornamental cherry hybrids with the canker pathogens, Pseudomonas syringae pvs syringae, morsprunorum races 1 and 2, and avii. Several Prunus accessions exhibited limited symptom development following inoculation with each of the pathogens, and this resistance extended to 16 P. syringae strains pathogenic on sweet cherry and plum. Resistance was associated with reduced bacterial multiplication after inoculation, a phenotype similar to that of commercial sweet cherry towards nonhost strains of P. syringae. Progeny resulting from a cross of a resistant ornamental species Prunus incisa with susceptible sweet cherry (P. avium) exhibited resistance indicating it is an inherited trait. Identification of accessions with resistance to the major bacterial canker pathogens is the first step towards characterizing the underlying genetic mechanisms of resistance and introducing these traits into commercial germplasm

Updated outcomes and impact of age with lenalidomide and low-dose dexamethasone or melphalan, prednisone, and thalidomide in the randomized, phase III FIRST trial

Purpose: This analysis of the FIRST trial in patients with newly diagnosed multiple myeloma (MM) ineligible for stem-cell transplantation examined updated outcomes and impact of patient age. Patients and Methods: Patients with untreated symptomatic MM were randomly assigned at a one-to-one-to-one ratio to lenalidomide plus low-dose dexamethasone until disease progression (Rd continuous), Rd for 72 weeks (18 cycles; Rd18), or melphalan, prednisone, and thalidomide (MPT; 72 weeks), stratified by age (≤ 75 v > 75 years), disease stage (International Staging System stage I/II v III), and country. The primary end point was progression-free survival. Rd continuous and MPT were primary comparators. Results: Between August 21, 2008, and March 7, 2011, 1,623 patients were enrolled (Rd continuous, n = 535; Rd18, n = 541; MPT, n = 547), including 567 (35%) age older than 75 years. Higher rates of advanced-stage disease and renal impairment were observed in patients older than 75 versus 75 years of age or younger. Rd continuous reduced the risk of progression or death compared with MPT by 31% (hazard ratio [HR], 0.69; 95% CI, 0.59 to 0.80; P <.001) overall, 36% (HR, 0.64; 95% CI, 0.53 to 0.77; P <.001) in patients age 75 years or younger, and 20% (HR, 0.80; 95% CI, 0.62 to 1.03; P =.084) in those age older than 75 years. Median overall survival was longer with Rd continuous than with MPT, including a 14-month difference in patients age older than 75 years. Progression-free survival with Rd18 was similar to that with MPT, and overall survival with Rd18 was marginally inferior to that with Rd continuous. Rates of grade 3 to 4 treatment-emergent adverse events were similar for Rd continuous-treated patients age 75 years or older and those age older than 75 years; however, older patients had more frequent lenalidomide dose reductions. Conclusion: Results support Rd continuous treatment as a new standard of care for stem-cell transplantation-ineligible patients with newly diagnosed MM of all ages. © 2016 by American Society of Clinical Oncology