Molecular mechanisms in grass-Epichloë interactions: towards endophyte driven farming to improve plant fitness and immunity

Morphological, Metabolomic and Genomic Evidences on Drought Stress Protective Functioning of the Endophyte Bacillus safensis Ni7

The metabolomic and genomic characterization of an endophytic Bacillus safensis Ni7 was carried out in this study. This strain has previously been isolated from the xerophytic plant Nerium indicum L. and reported to enhance the drought tolerance in Capsicum annuum L. seedlings. The effects of drought stress on the morphology, biofilm production, and metabolite production of B. safensis Ni7 are analyzed in the current study. From the results obtained, the organism was found to have multiple strategies such as aggregation and clumping, robust biofilm production, and increased production of surfactin homologues under the drought induced condition when compared to non-stressed condition. Further the whole genome sequencing (WGS) based analysis has demonstrated B. safensis Ni7 to have a genome size of 3,671,999 bp, N50 value of 3,527,239, and a mean G+C content of 41.58%. Interestingly the organism was observed to have the presence of various stress-responsive genes (13, 20U, 16U,160, 39, 17M, 18, 26, and ctc) and genes responsible for surfactin production (srfAA, srfAB, srfAC, and srfAD), biofilm production (epsD, epsE, epsF, epsG, epsH, epsI, epsK, epsL, epsM, epsN, and pel), chemotaxis (cheB_1, cheB_2, cheB_3, cheW_1, cheW_2 cheR, cheD, cheC, cheA, cheY, cheV, and cheB_4), flagella synthesis (flgG_1, flgG_2, flgG_3, flgC, and flgB) as supportive to the drought tolerance. Besides these, the genes responsible for plant growth promotion (PGP), including the genes for nitrogen (nasA, nasB, nasC, nasD, and nasE) and sulfur assimilation (cysL_1&L_2, cysI) and genes for phosphate solubilization (phoA, phoP_1& phoP_2, and phoR) could also be predicted. Along with the same, the genes for catalase, superoxide dismutase, protein homeostasis, cellular fitness, osmoprotectants production, and protein folding could also be predicted from its WGS data. Further pan-genome analysis with plant associated B. safensis strains available in the public databases revealed B. safensis Ni7 to have the presence of a total of 5391 gene clusters. Among these, 3207 genes were identified as core genes, 954 as shell genes and 1230 as cloud genes. This variation in gene content could be taken as an indication of evolution of strains of Bacillus safensis as per specific conditions and hence in the case of B. safensis Ni7 its role in habitat adaptation of plant is well expected. This diversity in endophytic bacterial genes may attribute its role to support the plant system to cope up with stress conditions. Overall, the study provides genomic evidence on Bacillus safensis Ni7 as a stress alleviating microbial partner in plants.

Methylome changes in Lolium perenne associated with long-term colonisation by the endophytic fungus Epichloë sp. LpTG-3 strain AR37

Epichloë spp. often form mutualistic interactions with cool-season grasses, such as Lolium perenne. However, the molecular mechanisms underlying this interaction remain poorly understood. In this study, we employed reduced representation bisulfite sequencing method (epiGBS) to investigate the impact of the Epichloë sp. LpTG-3 strain AR37 on the methylome of L. perenne across multiple grass generations and under drought stress conditions. Our results showed that the presence of the endophyte leads to a decrease in DNA methylation across genomic features, with differentially methylated regions primarily located in intergenic regions and CHH contexts. The presence of the endophyte was consistently associated with hypomethylation in plants across generations. This research sheds new light on the molecular mechanisms governing the mutualistic interaction between Epichloë sp. LpTG-3 strain AR37 and L. perenne. It underscores the role of methylation changes associated with endophyte infection and suggests that the observed global DNA hypomethylation in L. perenne may be influenced by factors such as the duration of the endophyte-plant association and the accumulation of genetic and epigenetic changes over time.

Comparative analysis of endophyte diversity of Dendrobium officinale lived on rock and tree

Dendrobium officinale usually lives on rock or tree, but their endophyte diversity has not yet been fully revealed? In this study, high-throughput sequencing technology was used to investigate the endophyte diversity of the roots of D. officinale lived on tree (Group 1-3, arboreal type) and rock (Group 4, lithophytic type). The results showed that their composition of endophytic fungi and bacteria were similar at phylum level, while their relative abundance were different. Their taxa composition and abundance of endophytes differed significantly among groups at the genus level. Alpha diversity of endophytic fungi of lithophytic type was higher than those from arboreal type, while there was no advantage in endophytic bacteria. Beta diversity revealed that the endophytic fungi tended to cluster in each group, but the endophytic bacteria were dispersed among the groups. LEfSe analysis found that the numbers of predicted endophyte biomarkers of lithophytic type were more than arboreal types at genus level, and the biomarkers varied among groups. Microbial network analysis revealed similarities and differences in the taxa composition and abundance of shared and special endophytes in each group. These results suggested that the root endophytes of lithophytic and arboreal D. officinale differed in diversity.

Whole-genome analysis revealed the growth-promoting mechanism of endophytic bacterial strain Q2H1 in potato plants

INTRODUCTION

Endophytes are non-pathogenic inhabitants of healthy plant tissues and have been found to promote plant growth and health. The endophytic bacterial strain Q2H1 was isolated from the roots of the potato and was identified to exhibit growth-promoting effects in potato plants.

METHODS

Whole-genome sequencing was performed to reveal the mechanism underlying its growth-promoting effect. The obtained sequencing data of approximately 5.65 MB encompassed 5,533 coding sequences. Of note, nine secondary metabolite gene clusters, including siderophore gene clusters, closely associated with plant growth promotion (PGP) were predicted by antiSMASH software. Comparative genomic analysis revealed that Q2H1 belongs to the genus Peribacillus. By gene function annotation, those genes related to plant growth-promoting activities, including indole-3-acetic acid (IAA) synthesis in tryptophan metabolism, siderophore biosynthetic activity, phosphate solubilization, nitrogen fixation, and related genes, were summarized. IAA (14.4 μg/ml) was presumptively produced by Q2H1 using the Salkowski colorimetric method. A total of five genes, namely, phoU, pstB, pstA1, pstC, and pstS, were annotated for phosphate solubilization, which is associated with the ability of the Q2H1 strain to solubilize phosphate under in vitro conditions.

RESULTS

It is revealed that genes in the Q2H1 genome associated with nitrogen fixation belonged to three groups, namely, nitrogen fixation (nifU, sufU, salA, and nifS), nitrogen metabolism (nirA, nrtB, and nasA), and glutamate synthesis (glnA, gltB, gltD, and gudB), supported by evidence that Q2H1 grew on medium without nitrogen. We have also identified a siderophore gene cluster located on the chromosome of Q2H1, including seven genes (viz., rbsR, rhbf, rhbE, rhbD, rhbC, rhbA, ddc, and an unknown gene). In the in vitro assay, a prominent brown circle around the colony was produced on the chrome azurol S medium at 48 and 72 h post-inoculation, indicating that the siderophore gene cluster in Q2H1 harbored the ability to produce siderophores.

CONCLUSION

In summary, these findings implied that identifying strain-specific genes for their metabolic pathways in bacterial endophytes may reveal a variety of significant functions of plant growth-promoting mechanisms.

Abscisic Acid May Play a Critical Role in the Moderating Effect of Epichloë Endophyte on Achnatherum inebrians under Drought Stress

Water scarcity is a major constraint that adversely affects plant development and growth. Abscisic acid (ABA) is a plant stress hormone that is rapidly synthesized and can induce stomatal closure to conserve water, thereby alleviating the drought stress of plants. The Epichloë endophyte enhances the drought tolerance of Achnatherum inebrians (drunken horse grass, DHG). To better understand how the Epichloë endophyte enhances drought tolerance, DHG plants without (EF) and with (EI), an Epichloë endophyte, were grown under 20% and 60% soil water conditions (SWC), and the leaves of the three treatments of EF and EI plants were sprayed with ABA solution (1 mg/L); fluridone (FLU), the ABA biosynthesis inhibitor solution (1 mg/L); and distilled water, respectively. Four-weeks later, the results indicated that the exogenous ABA application promoted plant growth, stomatal conductance, and photosynthetic rate, while the opposite effect occurred with plants sprayed with FLU. The differences between EI and EF plants in tiller number, height, chlorophyll content, stomata conductance, and photosynthetic rate were highest when sprayed with ABA. Thus, it is concluded that ABA might be involved in the moderating effect of Epichloë endophytes on DHG plants exposed to drought by maintaining growth and improving photosynthetic efficiency.

Identification of Three Epichloë Endophytes from Hordeum bogdanii Wilensky in China

Cool season grasses often form reciprocal symbiotic relationships with endophytic fungal species in genus Epichloë. In this study, we characterized three fungal endophytes isolated from the grass Hordeum bogdanii native to northwest China. Based on morphological characteristics and phylogenetic analyses of tefA, tubB, and actG sequences, we identified them as Epichloë sp. HboTG-2 (H. bogdanii Taxonomic Group 2: E. bromicola × E. typhina). Alkaloid synthesis related genes analysis showed that Epichloë sp. HboTG-2 may have the ability only to produce peramine which is toxic to insects but not to animals. In the process of this study, we did not observe sexual structures or epiphyllous growth on leaves of infected plants.