Endophytic bacterium Bacillus aryabhattai induces novel transcriptomic changes to stimulate plant growth.

In nature, plants interact with a wide range of microorganisms, and most of these microorganisms could induce growth through the activation of important molecular pathways. The current study evaluated whether the endophytic bacterium Bacillus aryabhattai encourages plant growth and the transcriptional changes that might be implicated in this effect. The endophytic bacterium promotes the growth of Arabidopsis and tobacco plants. The transcriptional changes in Arabidopsis plants treated with the bacterium were also identified, and the results showed that various genes, such as cinnamyl alcohol dehydrogenase, apyrase, thioredoxin H8, benzaldehyde dehydrogenase, indoleacetaldoxime dehydratase, berberine bridge enzyme-like and gibberellin-regulated protein, were highly expressed. Also, endophytic bacterial genes, such as arginine decarboxylase, D-hydantoinase, ATP synthase gamma chain and 2-hydroxyhexa-2,4-dienoate hydratase, were activated during the interaction. These findings demonstrate that the expression of novel plant growth-related genes is induced by interaction with the endophytic bacterium B. aryabhattai and that these changes may promote plant growth in sustainable agriculture.

Heat-killed endophytic bacterium induces robust plant defense responses against important pathogens.

Stress caused by pathogens strongly damages plants. Developing products to control plant disease is an important challenge in sustainable agriculture. In this study, a heat-killed endophytic bacterium (HKEB), Bacillus aryabhattai, is used to induce plant defense against fungal and bacterial pathogens, and the main defense pathways used by the HKEB to activate plant defense are revealed. The HKEB induced high protection against different pathogens through the salicylic and jasmonic acid pathways. We report the presence of gentisic acid in the HKEB for the first time. These results show that HKEBs may be a useful tool for the management of plant diseases.

High-throughput SuperSAGE for gene expression analysis of Nicotiana tabacum-Rhizoctonia solani interaction.

OBJECTIVE: The ubiquitous soil pathogen Rhizoctonia solani causes serious diseases in different plant species. Despite the importance of this disease, little is known regarding the molecular basis of susceptibility. SuperSAGE technology and next-generation sequencing were used to generate transcript libraries during the compatible Nicotiana tabacum-R. solani interaction. Also, we used the post-transcriptional silencing to evaluate the function of a group of important genes. RESULTS: A total of 8960 and 8221 unique Tag sequences identified as differentially up- and down-regulated were obtained. Based on gene ontology classification, several annotated UniTags corresponded to defense response, metabolism and signal transduction. Analysis of the N. tabacum transcriptome during infection identified regulatory genes implicated in a number of hormone pathways. Silencing of an mRNA induced by salicylic acid reduced the susceptibility of N. tabacum to R. solani. We provide evidence that the salicylic acid pathway was involved in disease development. This is important for further development of disease management strategies caused by this pathogen.

Expression of a Nicotiana tabacum pathogen-induced gene is involved in the susceptibility to black shank.

Many host genes induced during compatible plant-pathogen interactions constitute targets of pathogen virulence factors that act to suppress host defenses. In order to identify Nicotiana tabacum L. genes for pathogen-induced proteins involved in susceptibility to the oomycete Phytophthora parasitica var. nicotianae, we used SuperSAGE technology combined with next-generation sequencing to identify transcripts that were differentially upregulated during a compatible interaction. We identified a pathogen-induced gene (NtPIP) that was rapidly induced only during the compatible interaction. Virus-induced gene silencing of NtPIP reduced the susceptibility of N. tabacum to P. parasitica var. nicotianae. Additionally, transient expression of NtPIP in the resistant species Nicotiana megalosiphon Van Heurck & Mull. Arg. compromised the resistance to P. parasitica var. nicotianae. This pathogen-induced protein is therefore a positive regulator of the susceptibility response against an oomycete pathogen in tobacco.

NmDef02, a novel antimicrobial gene isolated from Nicotiana megalosiphon confers high-level pathogen resistance under greenhouse and field conditions.

Plant defensins are small cysteine-rich peptides that inhibit the growth of a broad range of microbes. In this article, we describe NmDef02, a novel cDNA encoding a putative defensin isolated from Nicotiana megalosiphon upon inoculation with the tobacco blue mould pathogen Peronospora hyoscyami f.sp. tabacina. NmDef02 was heterologously expressed in the yeast Pichia pastoris, and the purified recombinant protein was found to display antimicrobial activity in vitro against important plant pathogens. Constitutive expression of NmDef02 gene in transgenic tobacco and potato plants enhanced resistance against various plant microbial pathogens, including the oomycete Phytophthora infestans, causal agent of the economically important potato late blight disease, under greenhouse and field conditions.

Over-expression of a protein kinase gene enhances the defense of tobacco against Rhizoctonia solani.

To identify Nicotiana tabacum genes involved in resistance and susceptibility to Rhizoctonia solani, suppression subtractive hybridization was used to generate a cDNA library from transcripts that are differentially expressed during a compatible and incompatible interaction. This allowed the isolation of a protein kinase cDNA that was down-regulated during a compatible and up-regulated during an incompatible interaction. Quantitative RT-PCR analysis of this gene confirmed the differential expression patterns between the compatible and incompatible interactions. Over-expression of this gene in tobacco enhanced the resistance to damping-off produced by an aggressive R. solani strain. Furthermore, silencing of this protein kinase gene reduced the resistance to a non-aggressive R. solani strain. A set of reported tobacco-resistant genes were also evaluated in tobacco plants over-expressing and silencing the protein kinase cDNA. Several genes previously associated with resistance in tobacco, like manganese superoxide dismutase, Hsr203J, chitinases and phenylalanine ammonia-lyase, were up-regulated in tobacco plants over-expressing the protein kinase cDNA. Potentially, the protein kinase gene could be used to engineer resistance to R. solani in tobacco cultivars susceptible to this important pathogen.

Black shank resistant tobacco by silencing of glutathione S-transferase.

A glutathione S-transferase gene was amplified from cDNA of Nicotiana tabacum roots infected with Phytophthora parasitica var. nicotianae. The gene was cloned in sense and anti-sense orientation to an RNAi vector for induced gene silencing, and reduced expression of the gene was detected by RT-PCR. A statistically significant increase in resistance of N. tabacum to infection following gene silencing was found for glutathione S-transferase-silenced plants compared with control plants. Some defense genes were up-regulated in glutathione S-transferase-silenced plants during the interaction with the pathogen. This is the first evidence of the role of glutathione S-transferase as negative regulator of defense response.