Fusarium graminearum-induced changes in gene expression between Fusarium head blight-resistant and susceptible wheat cultivars.

Fusarium head blight (FHB), primarily caused by Fusarium graminearum Schw., is a destructive disease of wheat (Triticum aestivum L.). Although several genes related to FHB resistance have been reported, global analysis of gene expression in response to FHB infection remains to be explored. The expression patterns of transcriptomes from wheat spikes of FHB-resistant cultivar Ning 7840 and susceptible cultivar Clark were monitored during a period of 72 h after inoculation (hai) with F. graminearum. Microarray analysis, coupled with suppression subtractive hybridization technique, identified 44 significantly differentially expressed genes between cv. Ning 7840 and cv. Clark. More differentially expressed genes were identified from susceptible libraries than from resistance libraries. The up-regulation of defense-related genes in Ning 7840 relative to cultivar Clark occurred during early fungal stress (3-12 hai). Three genes, with unknown function that were up-regulated in cv. Ning 7840 at most time points investigated, might play an important role in enhancing FHB resistance.

Cold hardiness of wheat near-isogenic lines differing in vernalization alleles.

Four major genes in wheat (Triticum aestivum L.), with the dominant alleles designated Vrn-A1, Vrn-B1, Vrn-D1, and Vrn4, are known to have large effects on the vernalization response, but the effects on cold hardiness are ambiguous. Near-isogenic experimental lines (NILs) in a Triple Dirk (TD) genetic background with different vernalization alleles were evaluated for cold hardiness. Although TD is homozygous dominant for Vrn-A1 (formerly Vrn1) and Vrn-B1 (formerly Vrn2), four of the lines are each homozygous dominant for a different vernalization gene, and one line is homozygous recessive for all four vernalization genes. Following establishment, the plants were initially acclimated for 6 weeks in a growth chamber and then stressed in a low temperature freezer from which they were removed over a range of temperatures as the chamber temperature was lowered 1.3 degrees C h(-1). Temperatures resulting in no regrowth from 50% of the plants (LT(50)) were determined by estimating the inflection point of the sigmoidal response curve by nonlinear regression. The LT(50) values were -6.7 degrees C for cv. TD, -6.6 degrees C for the Vrn-A1 and Vrn4 lines, -8.1 degrees C for the Vrn-D1 (formerly Vrn3) line, -9.4 degrees C for the Vrn-B1 line, and -11.7 degrees C for the homozygous recessive winter line. The LT(50) of the true winter line was significantly lower than those of all the other lines. Significant differences were also observed between some, but not all, of the lines possessing dominant vernalization alleles. The presence of dominant vernalization alleles at one of the four loci studied significantly reduced cold hardiness following acclimation.

Evidence that the 37 kDa protein of Soil-borne wheat mosaic virus is a virus movement protein.

Experiments were conducted to determine if the 37 kDa protein (37K) of Soil-borne wheat mosaic virus (SBWMV) is a virus movement protein. First, evidence was obtained that indicated that 37K has the ability to move from cell to cell, similar to other virus movement proteins (MPs). Plasmids containing the GFP gene fused to the SBWMV 37K, the coat protein (CP) or the CP readthrough domain (RT) ORFs were delivered by biolistic bombardment to wheat and tobacco leaves. In wheat leaves, cell-to-cell movement of GFP-37K was observed, while GFP, GFP-CP and GFP-RT accumulated primarily in single cells. All fusion proteins accumulated in single cells in tobacco leaves. Thus, cell-to-cell movement is a specific property of 37K that occurs in SBWMV host plants. Subcellular accumulation of 37K was studied using SBWMV-infected and 37K-expressing transgenic wheat. In infected and transgenic wheat leaves, 37K accumulated in the cell wall, similar to other virus MPs, and in aggregates in the cytoplasm. Phylogenetic studies were conducted to compare the furovirus 37K proteins with members of the 30K superfamily of virus MPs. Amino acid sequences of the furovirus 37K proteins were aligned with the MPs from 43 representative viruses. The furovirus 37K proteins were found to reside in a clade that also contained the dianthovirus MPs. Combined, these data suggest that SBWMV 37K is probably a virus MP.

Tolerance of mannitol-accumulating transgenic wheat to water stress and salinity.

Previous work with model transgenic plants has demonstrated that cellular accumulation of mannitol can alleviate abiotic stress. Here, we show that ectopic expression of the mtlD gene for the biosynthesis of mannitol in wheat improves tolerance to water stress and salinity. Wheat (Triticum aestivum L. cv Bobwhite) was transformed with the mtlD gene of Escherichia coli. Tolerance to water stress and salinity was evaluated using calli and T(2) plants transformed with (+mtlD) or without (-mtlD) mtlD. Calli were exposed to -1.0 MPa of polyethylene glycol 8,000 or 100 mM NaCl. T(2) plants were stressed by withholding water or by adding 150 mM NaCl to the nutrient medium. Fresh weight of -mtlD calli was reduced by 40% in the presence of polyethylene glycol and 37% under NaCl stress. Growth of +mtlD calli was not affected by stress. In -mtlD plants, fresh weight, dry weight, plant height, and flag leaf length were reduced by 70%, 56%, 40%, and 45% compared with 40%, 8%, 18%, and 29%, respectively, in +mtlD plants. Salt stress reduced shoot fresh weight, dry weight, plant height, and flag leaf length by 77%, 73%, 25%, and 36% in -mtlD plants, respectively, compared with 50%, 30%, 12%, and 20% in +mtlD plants. However, the amount of mannitol accumulated in the callus and mature fifth leaf (1.7-3.7 micromol g(-1) fresh weight in the callus and 0.6-2.0 micromol g(-1) fresh weight in the leaf) was too small to protect against stress through osmotic adjustment. We conclude that the improved growth performance of mannitol-accumulating calli and mature leaves was due to other stress-protective functions of mannitol, although this study cannot rule out possible osmotic effects in growing regions of the plant.