A comparative proteome analysis reveals flagellin, chemotaxis regulated proteins and amylovoran to be involved in virulence differences between Erwinia amylovora strains

Erwinia amylovora is a Gram-negative bacterium that causes the destructive disease fire blight affecting most members of the Rosaceae family, of which apple and pear are economically the most important hosts. E. amylovora has been considered as a homogeneous species in whole, although significant differences in virulence patterns have been observed. However, the underlying causes of the differences in virulence remain to be discovered. In a first-time comparative proteomic approach using E. amylovora, 2D differential in-gel electrophoresis (DIGE) was used to identify proteins that could explain the gradual difference in virulence between four different strains. Two important proteins were identified, FliC and CheY, both involved in flagella structure, motility and chemotaxis, which were more abundant in the least virulent strain. In the highly virulent strains the protein GalF, involved in amylovoran production, was more abundant, which was consistent with the higher expression of the gene and the higher amylovoran content in this strain in vitro. Together, these results confirm the involvement of amylovoran in virulence, but also imply an indirect role of flagellin in virulence as elicitor of plant defence.

BIOLOGICAL SIGNIFICANCE

This research provides new insights into our current understanding of the virulence of Erwinia amylovora. This plant-pathogen is considered a homogeneous species although different strains show differences in virulence. Despite the efforts made on the genomic level which resulted in the discovery of virulence factors, the reason for the different virulence patterns between strains has not yet been identified. In our lab we used a comparative proteomic approach, which has never been published before, to identify proteins involved in these differences between strains and hereby possibly involved in virulence. Our results provide interesting insights in virulence and present us with the opportunity to glance into the proteome of E. amylovora.

Erwinia amylovora affects the phenylpropanoid-flavonoid pathway in mature leaves of Pyrus communis cv. Conférence

Flavonoids, which are synthesized by the phenylpropanoid-flavonoid pathway, not only contribute to fruit colour and photoprotection, they also may provide antimicrobial and structural components during interaction with micro-organisms. A possible response of this pathway was assessed in both mature and immature leaves of shoots of 2-year-old pear trees cv. Conférence, which were inoculated with the gram-negative bacterium Erwinia amylovora strain SGB 225/12, were mock-inoculated or were left untreated. The phenylpropanoid-flavonoid pathway was analysed by histological studies, by gene expression using RT-qPCR and by HPLC analyses of the metabolites at different time intervals after infection. Transcription patterns of two key genes anthocyanidin reductase (ANR) and chalcone synthase (CHS) related to the phenylpropanoid-flavonoid pathway showed differences between control, mock-inoculated and E. amylovora-inoculated mature leaves, with the strongest reaction 48 h after inoculation. The impact of E. amylovora was also visualised in histological sections, and confirmed by HPLC, as epicatechin -which is produced via ANR- augmented 72 h after inoculation in infected leaf tissue. Besides the effect of treatments, ontogenesis-related differences were found as well. The increase of certain key genes, the rise in epicatechin and the visualisation in several histological sections in this study suggest a non-negligible impact on the phenylpropanoid-flavonoid pathway in Pyrus communis due to inoculation with E. amylovora. In this study, we propose a potential role of this pathway in defence mechanisms, providing a detailed analysis of the response of this system attributable to inoculation with E. amylovora.

Chlorophyll a fluorescence imaging of ozone-stressed Brassica napus L. plants differing in glucosinolate concentrations

Brassicaceae are characterised by glucosinolates (GS), which appear to be involved not only in biotic but also in abiotic stress responses of plants. We investigated the effect of O (3) stress on leaf GS concentrations in two lines of BRASSICA NAPUS L., differing in GS content. Ozone fumigation decreased GS concentrations in leaves of B. NAPUS of one line. In control conditions, chlorophyll content, rates of saturating photosynthesis, and quantum yield of photosystem 2 differed between the two BRASSICA lines, but differences were smaller in O (3)-stress conditions, suggesting that the relationship between leaf GS concentration and sensitivity to abiotic stress merits further research. In agreement with other ecophysiological measurements, chlorophyll fluorescence imaging clearly distinguished both lines and in some cases also treatments. A method for analysis of fluorescence images accounting for the two-dimensional leaf heterogeneity is presented.

Apical dominance in Pssu-ipt-transformed tobacco

In Pssu-ipt-transformed tobacco, apical dominance was released by defoliation of the upper nodes, while the apex remained intact. After defoliation, the concentration of cytokinins (CKs) increased whereas IAA remained constant, evoking an increase in the CK/IAA ratio in the buds. Moreover, defoliation resulted in a tremendous increase in the concentrations of aromatic amines (AAs): tyramine (TYR), phenethylamine (PEA) and an as yet unidentified compound. Although the total aliphatic monoamine and polyamine (PA) concentration remained constant, putrescine (PUT) and spermidine (SPD) concentrations in the axillary buds decreased, whereas the concentration of spermine (SPM) increased. Similar changes in PAs and AAs could be observed in the buds of untransformed SR1 plants after decapitation, whereas defoliation without removal of the apex had no effect. This is the first report on the possible involvement of PAs and AAs in apical dominance.

Low-oxygen stress and water deficit induce cytosolic pyruvate orthophosphate dikinase (PPDK) expression in roots of rice, a C3 plant

Pyruvate orthophosphate dikinase (PPDK) is known for its role in C4 photosynthesis but has no established function in C3 plants. Abscisic acid, PEG and submergence were found to markedly induce a protein of about 97 kDa, identified by microsequencing as PPDK, in rice roots (C3). The rice genome was found to contain two ppdk loci, osppdka and osppdkb. We isolated osppdka cDNA, which encodes a cytosolic rice PPDK isoform of 96.6 kDa, that corresponded to the ABA-induced protein from roots. Western blot analysis showed a PPDK induction in roots of rice seedlings during gradual drying, cold, high salt and mannitol treatment, indicating a water deficit response. PPDK was also induced in the roots and sheath of submerged rice seedlings, and in etiolated rice seedlings exposed to an oxygen-free N2 atmosphere, which indicated a low-oxygen stress response. None of the stress treatments induced PPDK protein accumulation in the lamina of green rice seedlings. Ppdk transcripts were found to accumulate in roots of submerged seedlings, concomitant with the induction of alcohol dehydrogenase 1. Low-oxygen stress triggered an increase in PPDK activity in roots and etiolated rice seedlings, accompanied by increases in phosphoenolpyruvate carboxylase and malate dehydrogenase activities. The results indicate that cytosolic PPDK is involved in a metabolic response to water deficit and low-oxygen stress in rice, an anoxia-tolerant species.

Reinvestigation of the chlorophyll distribution among the chlorophyll-proteins and chlorophyll-protein complexes of Hordeum vulgare L

Solubilization of barley (Hordeum vulgare L.) thylakoid membranes with sodium dodecylsulphate plus sodium deoxycholate with or without Triton X-100 and subsequent fractionation in the polyacrylamide gel electrophoresis system described in this paper resulted: (1) in the resolution of the chlorophyll-proteins and chlorophyll-protein complexes commonly known as CP1a, CP1, LHCP(1), LHCP(2), CPa and LHCP(3); (2) in the highly increased stability of CP1 and CP1a, as judged by their chlorophyll content, (3) at the expense of the free pigment concentration (4) which could be reduced to a negligible amount. Some 40% of the total chlorophyll contained in the mature higher plant thylakoid membrane is associated with CP1 and CP1a and as already suggested before [19] no significant amount of free chlorophyll occurs in vivo.

Reinvestigation of the chlorophyll distribution among the chlorophyll-proteins and chlorophyll-protein complexes of Hordeum vulgare L

Solubilization of barley (Hordeum vulgare L.) thylakoid membranes with sodium dodecylsulphate plus sodium deoxycholate with or without Triton X-100 and subsequent fractionation in the polyacrylamide gel electrophoresis system described in this paper resulted: (1) in the resolution of the chlorophyll-proteins and chlorophyll-protein complexes commonly known as CP1a, CP1, LHCP(1), LHCP(2), CPa and LHCP(3); (2) in the highly increased stability of CP1 and CP1a, as judged by their chlorophyll content, (3) at the expense of the free pigment concentration (4) which could be reduced to a negligible amount. Some 40% of the total chlorophyll contained in the mature higher plant thylakoid membrane is associated with CP1 and CP1 a and as already suggested before [19] no significant amount of free chlorophyll occurs in vivo.