Dickeya zeae is the causal agent of the rice foot rot disease, but its mechanism of infection remains largely unknown. In this study, we identified and characterized a novel gene designated as zmsA. The gene encodes a large protein of 2,346 amino acids in length, which consists of multidomains arranged in the order of N-terminus, β-ketoacyl synthase, acyl transferase, acyl carrier protein, β-ketoacyl reductase, dehydratase. This multidomain structure and sequence alignment analysis suggest that ZmsA is a member of the polyketide synthase family. Mutation of zmsA abolished antimicrobial activity and attenuated the virulence of D. zeae. To determine the relationship between antimicrobial activity and virulence, active compounds were purified from D. zeae EC1 and were structurally characterized. This led to identification of two polyamino compounds, i.e., zeamine and zeamine II, that were phytotoxins and potent antibiotics. These results have established the essential role of ZmsA in zeamine biosynthesis and presented a new insight on the molecular mechanisms of D. zeae pathogenicity.

Erwinia chrysanthemi pv. zeae is one of the Erwinia chrysanthemi pathovars that infects on both dicotyledons and monocotyledons. However, little is known about the molecular basis and regulatory mechanisms of its virulence. By using a transposon mutagenesis approach, we cloned the genes coding for an E. chrysanthemi pv. zeae synthase of acyl-homoserine lactone (AHL) quorum-sensing signals (expI Ecz ) and a cognate response regulator (expR Ecz ). Chromatography analysis showed that expI Ecz encoded production of the AHL signal N-(3-oxo-hexanoyl)-homoserine lactone (OHHL). Null mutation of expI Ecz in the E. chrysanthemi pv. zeae strain EC1 abolished AHL production, increased bacterial swimming and swarming motility, disabled formation of multicell aggregates, and attenuated virulence of the pathogen on potato tubers. The mutation also marginally reduced the inhibitory activity of E. chrysanthemi pv. zeae on rice seed germination. The mutant phenotypes were rescued by either exogenous addition of AHL signal or in trans expression of expI Ecz . These data demonstrate that the AHL-type QS signal plays an essential role in modulation of E. chrysanthemi pv. zeae cell motility and the ability to form multicell aggregates and is involved in regulation of bacterial virulence.Erwinia chrysanthemi pv. zeae is the major pathogen responsible for bacterial stalk rot of maize around the world (20,29,31). The pathogen was also found to cause rice foot rot in Asian countries, including Japan, China, India, Indonesia, and South Korea (11,17). E. chrysanthemi pv. zeae is a member of the pathovars of the gram-negative bacterium Erwinia chrysanthemi, which has been divided, on the basis of its pathogenicity on host plants and certain biochemical and physiological differences, into six pathovars: pv. chrysanthemi, pv. dianthicola, pv. dieffenbachiae, pv. paradisiaca, pv. parthenii, and pv. zeae (7). The variations among these pathovars were subsequently verified by molecular genetic analysis (20,21). While the rationality of this pathovar classification is still under debate and a new scheme of classification has been proposed (29), in which E. chrysanthemi pv. zeae was delineated as a novel species, Dickeya zeae, the distinct status of E. chrysanthemi pv. zeae in different taxonomy schemes may reflect its unshakeable differences from other pathovars, which will hereby be collectively referred to as E. chrysanthemi strains for convenience and to be consistent with numerous previous studies. Recent constant outbreaks of rice foot rot disease caused by E. chrysanthemi pv. zeae have stirred serious concern (17); however, little is known about the molecular bases of its host specificity and the pathogenic mechanisms of this important pathovar of E. chrysanthemi.Among the closely related bacterial pathogens, a few E. crysanthemi strains that infect dicotyledonous plants, such as strains EC3937 and EC16, have been characterized extensively at biochemical and genetic levels. They are known to cause the soft rot disease that is characterized...

BackgroundDickeya zeae is a bacterial species that infects monocotyledons and dicotyledons. Two antibiotic-like phytotoxins named zeamine and zeamine II were reported to play an important role in rice seed germination, and two genes associated with zeamines production, i.e., zmsA and zmsK, have been thoroughly characterized. However, other virulence factors and its molecular mechanisms of host specificity and pathogenesis are hardly known.ResultsThe complete genome of D. zeae strain EC1 isolated from diseased rice plants was sequenced, annotated, and compared with the genomes of other Dickeya spp.. The pathogen contains a chromosome of 4,532,364 bp with 4,154 predicted protein-coding genes. Comparative genomics analysis indicates that D. zeae EC1 is most co-linear with D. chrysanthemi Ech1591, most conserved with D. zeae Ech586 and least similar to D. paradisiaca Ech703. Substantial genomic rearrangement was revealed by comparing EC1 with Ech586 and Ech703. Most virulence genes were well-conserved in Dickeya strains except Ech703. Significantly, the zms gene cluster involved in biosynthesis of zeamines, which were shown previously as key virulence determinants, is present in D. zeae strains isolated from rice, and some D. solani strains, but absent in other Dickeya species and the D. zeae strains isolated from other plants or sources. In addition, a DNA fragment containing 9 genes associated with fatty acid biosynthesis was found inserted in the fli gene cluster encoding flagellar biosynthesis of strain EC1 and other two rice isolates but not in other strains. This gene cluster shares a high protein similarity to the fatty acid genes from Pantoea ananatis.ConlusionOur findings delineate the genetic background of D. zeae EC1, which infects both dicotyledons and monocotyledons, and suggest that D. zeae strains isolated from rice could be grouped into a distinct pathovar, i.e., D. zeae subsp. oryzae. In addition, the results of this study also unveiled that the zms gene cluster presented in the genomes of D. zeae rice isolates and D. solani strains, and the fatty acid genes inserted in the fli gene cluster of strain EC1 were likely derived from horizontal gene transfer during later stage of bacterial evolution.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-015-1545-x) contains supplementary material, which is available to authorized users.

MicroRNAs (miRNAs) are small fragments of single-stranded RNA containing 18-24 nucleotides, and are generated from endogenous transcripts. MicroRNAs function in post-transcriptional gene silencing by targeting the 3′-untranslated region (UTR) of mRNAs, resulting in translational repression. We have developed a system to study the role of miRNAs in cell differentiation. We have found that one of the miRNAs tested in our system (miR-378, also called miR-378*) plays a role in modulating nephronectin-mediated differentiation in the osteoblastic cell line, MC3T3-E1. Nephronectin is an extracellular matrix protein, and we have demonstrated that its over-expression enhanced osteoblast differentiation and bone nodule formation. Furthermore, we found that the nephronectin 3′-untranslated region (3′UTR) contains a binding site for miR-378. Stable transfection of MC3T3-E1 cells with miR-378 inhibited cell differentiation. MC3T3-E1 cells stably transfected with nephronectin exhibited higher rates of differentiation and nodule formation as compared with cells transfected with nephronectin containing the 3′UTR in the early stages of development, suggesting that endogenous miR-378 is present and active. However, in the later stages of MC3T3-E1 development, the differentiation rates were opposite, with higher rates of differentiation and nodule formation in the cells over-expressing the 3′UTR of nephronectin. This appeared to be the consequence of competition between nephronectin and UDP-N-acetyl-alpha-D-galactosamine:polypeptide N-acetylgalactosaminyltransferase 7 (GalNAc-T7 or GalNT7) for miR-378 binding, resulting in increased GalNT7 activity, which in turn lead to increased nephronectin glycosylation and product secretion, thereby resulting in a higher rate of osteoblast differentiation.

SummaryMicroRNAs are known to play regulatory roles in gene expression associated with cancer development. We analyzed levels of the microRNA miR-24 in patients with breast carcinoma and found that miR-24 was higher in breast carcinoma samples than in benign breast tissues. We generated constructs expressing miR-24 and studied its functions using both in vitro and in vivo techniques. We found that the ectopic expression of miR-24 promoted breast cancer cell invasion and migration. In vivo experiments in mice indicated that the expression of miR-24 enhanced tumor growth, invasion into local tissues, metastasis to lung tissues and decreased overall mouse survival. In the miR-24-expressing cells and tumors, EGFR was highly phosphorylated, whereas expression of the phosphatases tyrosine-protein phosphatase non-receptor type 9 (PTPN9) and receptor-type tyrosine-protein phosphatase F (PTPRF) were repressed. We confirmed that miR-24 could directly target both PTPN9 and PTPRF. Consistent with this, we found that the levels of phosphorylated epidermal growth factor receptor (pEGFR) were higher whereas the levels of PTPN9 and PTPRF were lower in the patients with metastatic breast carcinoma. Ectopic expression of PTPN9 and PTPRF decreased pEGFR levels, cell invasion, migration and tumor metastasis. Furthermore, we found that MMP2, MMP11, pErk, and ADAM15 were upregulated, whereas TIMP2 was downregulated; all of which supported the roles of miR-24 in tumor invasion and metastasis. Our results suggest that miR-24 plays a key role in breast cancer invasion and metastasis. miR-24 could potentially be a target for cancer intervention.