Overproduction of the exopolysaccharide alginate causes mucoid colony morphology in Pseudomonas aeruginosa and is considered a major virulence determinant expressed by this organism during chronic respiratory infections in cystic fibrosis. One of the principal regulatory elements governing conversion to mucoidy in P. aeruginosa is AlgU, an alternative sigma factor which is 66% identical to and functionally interchangeable with E from Escherichia coli and Salmonella typhimurium. E has been implicated in the expression of systems enhancing bacterial resistance to environmental stress. In this study, we report that the gene encoding AlgU is transcribed in wild-type nonmucoid P. aeruginosa from multiple promoters (P 1 through P 5 ) that fall into three categories: (i) the P 1 and P 3 promoters, which display strong similarity to the ؊35 and ؊10 canonical sequences of E promoters and were found to be absolutely dependent on AlgU; (ii) the P 2 promoter, which was less active in algU mutants, but transcription of which was not completely abrogated in algU::Tc r cells; and (iii) the transcripts corresponding to P 4 and P 5 , which were not affected by inactivation of algU. Introduction of E. coli rpoE (encoding E ) or algU into P. aeruginosa algU::Tc r strains restored P 1 and P 3 transcription and brought the P 2 signal back to the wild-type level. The AlgU-dependent promoters P 1 and P 3 were inducible by heat shock in wild-type nonmucoid P. aeruginosa PAO1. At the protein level, induction of AlgU synthesis under conditions of extreme heat shock was detected by metabolic labeling of newly synthesized proteins, twodimensional gel analysis, and reaction with polyclonal antibodies raised against an AlgU peptide. Another AlgU-dependent promoter, the proximal promoter of algR, was also found to be induced by heat shock. Under conditions of high osmolarity, growth at elevated temperature induced alginate synthesis in the wild-type nonmucoid P. aeruginosa PAO1. Cumulatively, these results suggest that algU itself is subject to complex regulation and is inducible by extreme heat shock, that the alginate system is a subset of the stress-responsive elements controlled by AlgU, and that AlgU and, by extension, its homologs in other organisms (e.g., E in S. typhimurium) may play a role in bacterial virulence and adjustments to adverse growth conditions. Conversion of Pseudomonas aeruginosa to the mucoid phenotype in cystic fibrosis (CF) has become a paradigm of bacterial adaptation mechanisms in opportunistic pathogenesis (12,20,23). Mucoidy is the result of overproduction of the exopolysaccharide alginate and is considered a major virulence factor expressed by P. aeruginosa during chronic colonization of the lung in CF patients. The alginate biosynthetic pathway has been elucidated for the most part (6, 39). One of the critical alginate biosynthetic genes is algD, which encodes GDP mannose dehydrogenase, an enzyme catalyzing the first committed step in alginate synthesis (8). Transcriptional activation of this gene is necessary ...

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Pepper belongs to the Solanaceae family, which includes many important vegetable crops such as tomato, potato, and eggplant. Not only widely used as vegetables and spicy ingredients, pepper also has diverse applications in pharmaceutics, natural coloring agents, cosmetics, defense repellents, and as ornamental plants (Kim et al., 2014;Qin et al., 2014). Pepper is among the most widely cultivated and consumed vegetables in the world, with annual production reaching to 38 million tons in 2011 (www.fao. org). Pepper fruits have significant diversity in morphology and color, and they provide good models for fruit developmental biology (Paran and van der Knaap, 2007;Rivera et al., 2016). Like all other crops, pepper plants are often confronted with different pathogens and pests (Pernezny et al., 2003), and diverse abiotic stress conditions, which necessitate basic studies on the mechanisms of pepper plants responding to various stimuli to facilitate breeding efforts for tolerant cultivars.

BackgroundAbiotic stresses cause severe loss of crop production. Among them, drought is one of the most frequent environmental stresses, which limits crop growth, development and productivity. Plant drought tolerance is fine-tuned by a complex gene regulatory network. Understanding the molecular regulation of this polygenic trait is crucial for the eventual success to improve plant yield and quality. Recent studies have demonstrated that microRNAs play critical roles in plant drought tolerance. However, little is known about the microRNA in drought response of the model plant tomato. Here, we described the profiling of drought-responsive microRNA and mRNA in tomato using high-throughput next-generation sequencing.ResultsDrought stress was applied on the seedlings of M82, a drought-sensitive cultivated tomato genotype, and IL9–1, a drought-tolerant introgression line derived from the stress-resistant wild species Solanum pennellii LA0716 and M82. Under drought, IL9–1 performed superior than M82 regarding survival rate, H2O2 elimination and leaf turgor maintenance. A total of four small RNA and eight mRNA libraries were constructed and sequenced using Illumina sequencing technology. 105 conserved and 179 novel microRNAs were identified, among them, 54 and 98 were differentially expressed upon drought stress, respectively. The majority of the differentially-expressed conserved microRNAs was up-regulated in IL9–1 whereas down-regulated in M82. Under drought stress, 2714 and 1161 genes were found to be differentially expressed in M82 and IL9–1, respectively, and many of their homologues are involved in plant stress, such as genes encoding transcription factor and protein kinase. Various pathways involved in abiotic stress were revealed by Gene Ontology and pathway analysis. The mRNA sequencing results indicated that most of the target genes were regulated by their corresponding microRNAs, which suggested that microRNAs may play essential roles in the drought tolerance of tomato.ConclusionIn this study, numerous microRNAs and mRNAs involved in the drought response of tomato were identified using high-throughput sequencing, which will provide new insights into the complex regulatory network of plant adaption to drought stress. This work will also help to exploit new players functioning in plant drought-stress tolerance.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-017-3869-1) contains supplementary material, which is available to authorized users.

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