A single-copy extensin gene (atExt1) has been isolated from Arabidopsis thaliana (L.) Heynh. The deduced amino acid sequence consists of 374 amino acids which are organised into highly ordered repeating blocks in which Ser(Pro)4 and Ser(Pro)3 motifs alternate. Two copies of the Tyr-X-Tyr-Lys motif and 13 copies of the Val-Tyr-Lys motif are present, showing that this extensin may be highly cross-linked, possessing the capacity for both intra and inter-molecular bond formation. The gene atExt1 is normally expressed in the root and is silent in the leaf; wounding reverses this pattern, turning on the gene in the leaf and repressing it in the root. The promoter contains motifs which have been found to activate plant defence genes in response to salicylic acid, abscisic acid and methyl jasmonate; when these compounds are applied to the roots, the atExt1 gene is activated in the leaf.

Although mitogen-activated protein kinases (MAPKs) have been shown to be activated by a wide range of biotic and abiotic stimuli in diverse plant species, few in vivo substrates for these kinases have been identified. While studying proteins that are differentially phosphorylated upon treatment of Arabidopsis suspension cultures with the general bacterial elicitor peptide flagellin-22 (flg22), we identified two proteins with endogenous nickel binding properties that become phosphorylated after flg22 elicitation. These highly related proteins, AtPHOS32 and AtPHOS34, show similarity to bacterial universal stress protein A. We identified one of the phosphorylation sites on AtPHOS32 by nanoelectrospray ionization tandem mass spectrometry. Phosphorylation in a phosphoSer-Pro motif indicated that this protein may be a substrate of MAPKs. Using in vitro kinase assays, we confirmed that AtPHOS32 is a substrate of both AtMPK3 and AtMPK6. Specificity of phosphorylation was demonstrated by site-directed mutagenesis of the first phosphorylation site. In addition, immunosubtraction of both MAPKs from protein extracts removed detectable kinase activity toward AtPHOS32, indicating that the two MAPKs were the predominate kinases recognizing the motif in this protein. Finally, the target phosphorylation site in AtPHOS32 is conserved in AtPHOS34 and among apparent orthologues from many plant species, indicating that phosphorylation of these proteins by AtMPK3 and AtMPK6 orthologues has been conserved throughout evolution.Plants recognize potential microbial pathogens through microbial-associated molecular patterns (MAMPs; 5 1, 2).MAMP perception by defined host cell surface receptors initiates MAMP-triggered immunity, the first line of defense contributing to the arrest of microbial growth. The best characterized MAMP perception system in plants is the recognition of bacterial flagellin or flg22, the bioactive peptide from a highly conserved 22-amino-acid region of the protein (3), by the receptor kinase flagellin-sensitive 2 (FLS2) (4). Recognition of flg22 by FLS2 initiates intracellular signaling that results in a number of rapid responses thought to contribute to defense(s) against the invading microbe (5).Among the most studied of these early responses is the rapid activation of mitogen-activated protein kinases (MAPKs). MAPKs are the final components of signaling cascades, activated by upstream MAPK kinases (MAPKKs), which are also activated by other upstream kinases, MAPKK kinases (MAPKKKs) (6 -8). In Arabidopsis, flg22 has been shown to activate two MAPKs, AtMPK3 and AtMPK6 (9, 10). Moreover, plants with reduced levels of AtMPK6 displayed increased susceptibility to infection by virulent and avirulent strains of the bacterial pathogen, Pseudomonas syringae, indicating that signaling via AtMPK6 plays a critical role during defense responses (11).Although activation of MAPKs in response to a wide range of biotic and abiotic stimuli has been well characterized (8), relatively little is known about the substrates of these kin...

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A single copy of the N-acetyl-L-glutamate synthase gene (SlNAGS1) has been isolated from tomato. The deduced amino acid sequence consists of 604 amino acids and shows a high level of similarity to the predicted Arabidopsis NAGS1 and NAGS2 proteins. Furthermore, the N-terminus ArgB domain and the C-terminus ArgA domain found in SlNAGS1 are similar to the structural arrangements that have been reported for other predicted NAGS proteins. SlNAGS1 was expressed at high levels in all aerial organs, and at basic levels in seeds, whereas it was not detected at all in roots. SlNAGS1 transcript accumulation was noticed transiently in tomato fruit at the red-fruit stage. In addition, an increase of SlNAGS1 transcripts was detected in mature green tomato fruit within the first hour of exposure to low oxygen concentrations. Transgenic Arabidopsis plants have been generated expressing the SlNAGS1 gene under the control of the cauliflower mosaic virus (CaMV) 35S promoter. Three homozygous transgenic lines expressing the transgene (lines 1-7, 3-8, and 6-5) were evaluated further. All three transgenic lines showed a significant accumulation of ornithine in the leaves with line 3-8 exhibiting the highest concentration. The same lines demonstrated higher germination ability compared to wild-type (WT) plants when subjected to 250 mM NaCl. Similarly, mature plants of all three transgenic lines displayed a higher tolerance to salt and drought stress compared to WT plants. Under most experimental conditions, transgenic line 3-8 performed best, while the responses obtained from lines 1-7 and 6-5 depended on the applied stimulus. To our knowledge, this is the first plant NAGS gene to be isolated, characterized, and genetically modified.

We detail the expression of the Arabidopsis thaliana (L.) Heynh. atExt1 extensin gene. atExt1 is normally expressed in roots and inflorescences, and is induced by wounding, exogenously supplied salicylic acid, methyl jasmonate, auxins and brassinosteroids. Northern assays and histochemical analysis of transgenics expressing an atExt1:: gus fusion show that this gene is also induced by the brassica pathogen Xanthomonas campestris pv. campestris and that this induction is restricted to tissues close to the site of infection. Expression at regions of abscission and senescence also implicates atExt1 in these important developmental processes.

ABSTRACT. Quince is a deciduous tree known to the countries around the Mediterranean since antiquity. Nowadays, quince is used as an ornamental plant, and as a rootstock for pear trees, with its fruit being appreciated mainly for production of jam and sweets rather than for raw consumption. Quince leaves contain compounds with antioxidant, antimicrobial and anticancerous properties that have been the focus of recent research on pharmaceutical and medical uses as well as for food preservatives. An orchard has been established in Greece, composed of quince varieties (Cydonia oblonga, N = 49) collected from different sites of the country (mainly from home gardens), constituting a unique quince gene bank collection for southeast Europe. We made a phenotypic analysis using 26 morphological plus seven agronomical descriptors coupled with molecular techniques in order to examine the genetic diversity within the collection. Principal component analysis using the 33 descriptors identified 10 components explaining the existence of more than 70% of the total variation. Subsequent cluster analysis classified most of the previously identified productive varieties of the quince orchard in the same clade of a dendrogram. Molecular analysis generated by 13 inter-simple sequence repeat primers amplified 139 bands, including 109 polymorphic bands, indicating a level of polymorphism of 79%; mean gene diversity was calculated to be 0.309. Using stepwise multiple regression analysis, a number of markers significantly associated with fire blight susceptibility, yield, mean fruit weight, citric acid content, soluble solid content, and fruit drop were identified. Hence, data extracted by multiple regression analysis could be useful in marker-assisted breeding programs, especially when no previous genetic information is available.

In a germplasm bank collection the conservation and characterization of genetic resources is a prerequisite in order to use the material in breeding projects aiming the creation of new cultivars. In the present study, 54 Prunus salicina domestica and Prunus domestica genotypes (including seven Greek cultivars), maintained in the ex situ National Genebank Collection of Greece, were classified using microsatellite (simple sequence repeat, SSR) markers on high resolution melting (HRM) analysis. The SSR primer pairs were chosen from the published literature as originally designed on Prunus species. This combined approach was used to genotype all plum accessions of the collection highlighting the benefits of either method (HRM and SSRs) for cultivar identification. Dendrograms for P. domestica and P. salicina and a combined one with all the genotypes assayed were produced. A total of 15 from the 19 P. domestica accessions analysed, including all the Greek accessions but 'Avgati Skopelou', were grouped into the same clade in the combined dendrogram, whereas the remaining four were dispersed into the P. salinica clades. Bayesian structure analysis confirmed that 'Avgati Skopelou' differs from the rest of the Greek plum cultivars since it was not grouped into the same cluster. The combination of HRM and SSRs, provided a considerably faster, cost-effective, closed-tube microsatellite genotyping method for molecular characterization of plum cultivars.

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