Methyl jasmonate (MeJA) is widely used as a model chemical to study hypersensitive responses to biotic stress impacts in plants. Elevated levels of methyl jasmonate induce jasmonate-dependent defense responses, associated with a decline in primary metabolism and enhancement of secondary metabolism of plants. However, there is no information of how stress resistance of plants, and accordingly the sensitivity to exogenous MeJA can be decreased by endophytic plant growth promoting rhizobacteria (PGPR) harboring ACC (1-aminocyclopropane-1-carboxylate) deaminase. In this study, we estimated stress alleviating potential of endophytic PGPR against MeJA-induced plant perturbations through assessing photosynthetic traits and stress volatile emissions. We used mild (5 mM) to severe (20 mM) MeJA and endophytic plant growth promoting rhizobacteria Burkholderia vietnamiensis CBMB40 and studied how MeJA and B. vietnamiensis treatments influenced temporal changes in photosynthetic characteristics and stress volatile emissions. Separate application of MeJA markedly decreased photosynthetic characteristics and increased lipoxygenase pathway (LOX) volatiles, volatile isoprenoids, saturated aldehydes, lightweight oxygenated compounds (LOC), geranyl-geranyl diphosphate pathway (GGDP) volatiles, and benzenoids. However, MeJA-treated leaves inoculated by endophytic bacteria B. vietnamiensis had substantially increased photosynthetic characteristics and decreased emissions of LOX, volatile isoprenoids and other stress volatiles compared with non-inoculated MeJA treatments, especially at later stages of recovery. In addition, analysis of leaf terpenoid contents demonstrated that several mono- and sesquiterpenes were de novo synthesized upon MeJA and B. vietnamiensis applications. This study demonstrates that foliar application of endophytic bacteria B. vietnamiensis can potentially enhance resistance to biotic stresses and contribute to the maintenance of the integrity of plant metabolic activity.

Microbial community composition and diversity of agricultural soils primarily depend on management practices. The application of compost on agricultural fields is known to increase soil fertility, which can also help to enhance agricultural productivity. The effects of long-term application of compost along with nitrogen (N), phosphorus (P), and potassium (K) (+Compost) on soil bacterial diversity and community profiles were assessed by amplicon sequencing targeting the 16S rRNA gene of bacteria and compared with those on soils that received only NPK but not compost (−Compost). Ordination plot showed treatments to cluster differently, implying changes in community composition, which were validated with taxonomical data showing Firmicutes, Actinobacteria, and their related classes to be significantly higher in +Compost than in −Compost soils. The predicted abundance of functional genes related to plant growth promotion, development, and decomposition was significantly higher in compost-amended soil than in soils without compost. The results are of particular importance as they provide insights into designing management practices to promote agricultural sustainability.

Endosymbiotic associations between hornworts and nitrogen-fixing cyanobacteria form when the plant is limited for combined nitrogen (N). We generated RNA-seq data to examine temporal gene expression patterns during the culturing of N-starved Anthoceros punctatus in the absence and the presence of symbiotic cyanobacterium Nostoc punctiforme. In symbiont-free A. punctatus gametophytes, N starvation caused downregulation of chlorophyll content and chlorophyll fluorescence characteristics as well as transcription of photosynthesis-related genes. This downregulation was reversed in A. punctatus cocultured with N. punctiforme, corresponding to the provision by the symbiont of N₂-derived NH₄⁺, which commenced within 5 days of coculture and reached a maximum by 14 days. We also observed transient increases in transcription of ammonium and nitrate transporters in a N. punctiforme–dependent manner as well as that of a SWEET transporter that was initially independent of N₂-derived NH₄⁺. The temporal patterns of differential gene expression indicated that N. punctiforme transmits signals that impact gene expression to A. punctatus both prior to and after its provision of fixed N. This study is the first illustrating the temporal patterns of gene expression during establishment of an endosymbiotic nitrogen-fixing association in this monophyletic evolutionary lineage of land plants. [ ] Copyright © 2022 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .

Endosymbiotic association between hornworts and dinitrogen-fixing cyanobacteria form when the plant is limited for combined nitrogen (N). We generated RNA-Seq data to examine the temporal gene expression patterns during culture of N-starved Anthoceros punctatus in the absence and presence of the symbiotically competent cyanobacterium Nostoc punctiforme . Symbiotic nitrogenase activity commenced within 5 days of coculture reaching a maximal by 14 days. In symbiont-free gametophytes, chlorophyll content, chlorophyll fluorescence characteristics and transcription of genes encoding light harvesting and reaction center proteins, as well as the small subunit of ribulose-bisphosphate-carboxylase/oxygenase, were downregulated. The downregulation was complemented in a temporal pattern corresponding to the N . punctiforme provision of N ₂ -derived ammonium. The impairment and complementation of photosynthesis was the most distinctive response of A . punctatus to N-starvation. Increases in transcription of ammonium and nitrate transporters and their N . punctiforme -dependent complementation was also observed. The temporal patterns of differential gene expression indicated N . punctiforme transmits signals to A . punctatus both prior to, and after its provision of fixed N. This is the only known temporal transcriptomic study during establishment of a symbiotic nitrogen-fixing association in this monophyletic evolutionary lineage of land plants. Highlights: Temporal RNA-Seq analysis revealed how symbiotic cyanobacteria impact plant partners’ global gene expression and elucidated the nature of bidirectional communications between the partners