Order of microbial succession affects rhizobia-mediated biocontrol efforts against Phytophthora root rot.

The management of soilborne root diseases in pulse crops is challenged by a limited range of resistance sources and often a complete absence of in-crop management options. Therefore, alternative management strategies need to be developed. We evaluated disease limiting interactions between the rhizobia species Mesorhizobium ciceri, and the oomycete pathogen Phytophthora medicaginis, which causes Phytophthora root rot (PRR) of chickpea (Cicer arietinum). For the PRR susceptible var. Sonali plants, post-pathogen M. ciceri inoculation significantly improved probability of plant survival when compared to P. medicaginis infected plants only pre-inoculated with M. ciceri (75 % versus 35 %, respectively). Potential mechanisms for these effects were investigated: rhizobia inoculation benefits to plant nodulation were not demonstrated, but the highest nodule N-fixation activity of P. medicaginis inoculated plants occurred for the post-pathogen M. ciceri treatment; rhizobia inoculation treatment did not reduce lesion development but certain combinations of microbial inoculation led to significant reduction in root growth. Microcosm studies, however, showed that the presence of M. ciceri reduced growth of P. medicaginis isolates. Putative chickpea disease resistance gene expression was evaluated using qPCR in var. Sonali roots. When var. Sonali plants were treated with M. ciceri post-P. medicaginis inoculation, the gene regulation in the plant host became more similar to PRR moderately resistant var. PBA HatTrick. These results suggest that M. ciceri application post P. medicaginis inoculation may improve plant survival by inducing defense responses similar to a PRR moderately resistant chickpea variety. Altogether, these results indicate that order of microbial succession can significantly affect PRR plant survial in susceptible chickpea under controlled conditions and improved plant survival effects are due to a number of different mechanisms including improved host nutrition, through direct inhibiton of pathogen growth, as well as host defense priming.

First Report of Wheat streak mosaic virus on Wheat in New Zealand.

In August of 2005, seeds of wheat (Triticum aestivum) breeding line 6065.3 tested positive for Wheat streak mosaic virus (WSMV; genus Tritimovirus) by a WSMV-specific reverse transcription (RT)-PCR assay (2). The sequence of the 200-bp amplicon (GenBank Accession No. FJ434246) was 99% identical with WSMV isolates from Turkey and the United States (GenBank Accession Nos. AF454455 and AF057533) and 96 to 97% identical to isolates from Australia (GenBank Accession Nos. DQ888801 to DQ888805 and DQ462279), which belong to the subclade D (1). As a result, an extensive survey of three cereal experimental trials and 105 commercial wheat crops grown on the South Island of New Zealand was conducted during the 2005-2006 summer to determine the distribution of WSMV. Wherever possible, only symptomatic plants were collected. Symptoms on wheat leaf samples ranged from very mild mosaic to symptomless. In total, 591 leaf samples suspected to be symptomatic were tested for WSMV by a double-antibody sandwich (DAS)-ELISA (DSMZ, Braunschweig, Germany). Of the 591 symptomatic samples, 81 tested positive. ELISA results were confirmed by RT-PCR with novel forward (WSMV-F1; 5'-TTGAGGATTTGGAGGAAGGT-3') and reverse (WSMV-R1; 5'-GGATGTTGCCGAGTTGATTT-3') primers designed to amplify a 391-nt fragment encoding a region of the P3 and CI proteins. Total RNA was extracted from the 81 ELISA-positive leaf samples using the Plant RNeasy Kit (Qiagen Inc., Chatsworth, CA). The expected size fragment was amplified from each of the 81 ELISA-positive samples. The positive samples represent 30 of 56 wheat cultivars (54%) collected from 28 of 108 sites (26%) sampled in the growing regions from mid-Canterbury to North Otago. These results suggest that WSMV is widespread in New Zealand both geographically and within cultivars. WSMV is transmitted by the wheat curl mite (Aceria tosichella) (3), which had not been detected in New Zealand despite repeated and targeted surveys. WSMV is of great economic importance in some countries, where the disease has been reported to cause total yield loss (3). Although WSMV is transmitted by seeds at low rates (0.1 to 0.2%) (4), it is the most likely explanation of the spread of the disease in New Zealand. References: (1) G. I. Dwyer et al. Plant Dis. 91:164, 2007. (2) R. French and N. L. Robertson. J. Virol. Methods 49:93, 1994. (3) R. French and D. C. Stenger. Descriptions of Plant Viruses. Online publication. No. 393, 2002. (4) R. A. C. Jones et al. Plant Dis. 89:1048, 2005.

Crystallization of the NADP-dependent beta-keto acyl carrier protein reductase from Escherichia coli.

The NADP-dependent beta-keto acyl carrier protein reductase (BKR) from E. coli has been crystallized by the hanging-drop method of vapour diffusion using poly(ethylene glycol) of average molecular weight 1450. The crystals belong to the hexagonal space group P6122 or P6522 with unit-cell dimensions a = b = 67.8, c = 355.8 A. Calculated values for Vm and consideration of the packing suggest that the asymmetric unit contains a dimer. BKR catalyses the first reductive step in the elongation cycle of fatty-acid biosynthesis. It shares extensive sequence homology with the enzyme which catalyzes the second reductive step in the cycle, enoyl acyl carrier protein reductase (ENR), and thus provides an opportunity to study the evolution of enzyme function in a metabolic pathway. The structure determination will permit the analysis of the molecular basis of its catalytic mechanism and substrate specificity.

Crystallization of Escherichia coli enoyl reductase and its complex with diazaborine.

Recent work has shown that the NADH-dependent enoyl acyl carrier protein reductase from Escherichia coli is the target for diazaborine, an antibacterial agent. This enzyme has been crystallized by the hanging-drop method of vapour diffusion complexed with NAD(+) and in the presence and absence of a thieno diazaborine. The crystals grown in the absence of diazaborine (form A) are in the space group P2(1) with unit-cell dimensions a = 74.0, b = 81.2, c = 79.0 A and beta = 92.9 degrees, and with a tetramer in the asymmetric unit, whilst those grown in the presence of diazaborine (form B) are in the space group P6(1)22 (or P6(5)22) with unit-cell dimensions a = b = 80.9 and c = 328.3 A, and with a dimer in the asymmetric unit. The structure determination of this enzyme in the presence of diazaborine will provide information on the nature of the drug binding site and contribute to a programme of rational drug design.