Take-all, which is caused by the fungal pathogen, Gaeumannomyces graminis var. tritici (Ggt), is an important soil-borne root rot disease of wheat occurring worldwide. However, the genetic basis of Ggt pathogenicity remains unclear. In this study, transcriptome sequencing for Ggt in axenic culture and Ggt-infected wheat roots was performed using Illumina paired-end sequencing. Approximately 2.62 and 7.76 Gb of clean reads were obtained, and 87% and 63% of the total reads were mapped to the Ggt genome for RNA extracted from Ggt in culture and infected roots, respectively. A total of 3,258 differentially expressed genes (DEGs) were identified with 2,107 (65%) being 2-fold up-regulated and 1,151 (35%) being 2-fold down-regulated between Ggt in culture and Ggt in infected wheat roots. Annotation of these DEGs revealed that many were associated with possible Ggt pathogenicity factors, such as genes for guanine nucleotide-binding protein alpha-2 subunit, cellulase, pectinase, xylanase, glucosidase, aspartic protease and gentisate 1, 2-dioxygenase. Twelve DEGs were analyzed for expression by qRT-PCR, and could be generally divided into those with high expression only early in infection, only late in infection and those that gradually increasing expression over time as root rot developed. This indicates that these possible pathogenicity factors may play roles during different stages of the interaction, such as signaling, plant cell wall degradation and responses to plant defense compounds. This is the first study to compare the transcriptomes of Ggt growing saprophytically in axenic cultures to it growing parasitically in infected wheat roots. As a result, new candidate pathogenicity factors have been identified, which can be further examined by gene knock-outs and other methods to assess their true role in the ability of Ggt to infect roots.
We studied the responses of the activities of adenosine-triphosphate (ATP) sulfurylase (ATPS) and serine acetyltransferase (SAT) to cadmium (Cd) levels and treatment time in hyperaccumulating ecotype (HE) Sedum alfredii Hance, as compared with its non-hyperaccumulating ecotype (NHE). The results show that plant growth was inhibited in NHE but promoted in HE when exposed to high Cd level. Cd concentrations in leaves and shoots rapidly increased in HE rather than in NHE, and they became much higher in HE than in NHE along with increasing treatment time and Cd supply levels. ATPS activity was higher in HE than in NHE in all Cd treatments, and increased with increasing Cd supply levels in both HE and NHE when exposed to Cd treatment within 8 h. However, a marked difference of ATPS activity between HE and NHE was found with Cd treatment for 168 h, where ATPS activity increased in HE but decreased in NHE. Similarly, SAT activity was higher in HE than in NHE at all Cd treatments, but was more sensitive in NHE than in HE. Both ATPS and SAT activities in NHE leaves tended to decrease with increasing treatment time after 8 h at all Cd levels. The results reveal the different responses in sulfur assimilation enzymes and Cd accumulation between HE and NHE. With increasing Cd stress, the activities of sulfur assimilation enzymes (ATPS and SAT) were induced in HE, which may contribute to Cd accumulation in the hyperaccumulator Sedum alfredii Hance.
The Lhcb2 gene from hyperaccumulator Sedum alfredii was up-regulated more than three-fold while the non-hyperaccumulator accumulated one or two-fold higher amount of the mRNA than control plants under different concentrations of Cd(2+) for 24 h. Lhcb2 expression was up-regulated more than five-fold in a non-hyperaccumulator S. alfredii when exposed to 2 μM Cd(2+) or 50 μM Zn(2+) for 8 d and the hyperaccumulator had over two-fold more mRNA abundance than the control plants. Over-expression of SaLhcb2 increased the shoot biomass by 14-41% and the root biomass by 21-57% without Cd(2+) treatment. Four transgenic tobacco lines (L5, L7, L10 and L11) possessed higher shoot biomass than WT plants with Cd(2+). Four transgenic lines (L7, L8, L10 and L11) accumulated 6-35% higher Cd(2+) amounts in shoots than the wild type plants.
Sedum alfredii Hance has been identified as zinc (Zn) and cadmium (Cd) co-hyperaccumulator. In this paper the relationships of Zn or Cd hyperaccumulation to the generation and the role of H 2 O 2 in Sedum alfredii H. were examined. The results show that Zn and Cd contents in the shoots of Sedum alfredii H. treated with 1000 μmol/L Zn 2+ and/or 200 μmol/L Cd 2+ increased linearly within 15 d. Contents of total S, glutathione (GSH) and H 2 O 2 in shoots also increased within 15 d, and then decreased. Total S and GSH contents in shoots were higher under Cd 2+ treatment than under Zn 2+ treatment. However, reverse trends of H 2 O 2 content in shoots were obtained, in which much higher H 2 O 2 content was observed in Zn 2+ -treated shoots than in Cd 2+ -treated shoots. Similarly, the microscopic imaging of H 2 O 2 accumulation in leaves using H 2 O 2 probe technique showed that much higher H 2 O 2 accumulation was observed in the Zn 2+ -treated leaf than in the Cd 2+ -treated one. These results suggest that there are different responses in the generation of H 2 O 2 upon exposure to Zn 2+ and Cd 2+ for the hyperaccumulator Sedum alfredii H. And this is the first report that the generation of H 2 O 2 may play an important role in Zn hyperaccumulation in the leaves. Our results also imply that GSH may play an important role in the detoxification of dissociated Zn/Cd and the generation of H 2 O 2 .
In this study, the heavy metal contents were detected in plants of Sedum alfredii and soils from Pb/Zn mined area and non-mined area, and a dendrogram was generated by using RAPD methods based on the hyperaccumulating ecotype (HE), the non-hyperaccumulating ecotype (NHE) and other species of Sedum. The results showed that the available Pb of the Pb/Zn mined soil was 77-fold higher, and available Zn and Cd were 10-fold and 16-fold higher in the mined soil than in the non-mined soil, respectively. The dendrogram showed that the HE S. alfredii was the nearest relative to NHE S. alfredii. However, genomic variation of two ecotypes was still notable, indicating that heavy metal stress had great impacts on the genetic diversity and plant evolution, and HE may be a mutant from the NHE. Ten RAPD bands were observed only in the HE as compared with other species of Sedum. The character of Zn/Cd hyperaccumulation in HE appeared to be related to SH-containing compounds and resist osmotic stress, and also many unknown genes.
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