Effects of Epichloë sinica on Roegneria kamoji seedling physiology under PEG-6000 simulated drought stress

Endophytes Alleviate Drought-Derived Oxidative Damage in Achnatherum inebrians Plants Through Increasing Antioxidants and Regulating Host Stress Responses

Endophytes generally increase antioxidant contents of plants subjected to environmental stresses. However, the mechanisms by which endophytes alter the accumulation of antioxidants in plant tissues are not entirely clear. We hypothesized that, in stress situations, endophytes would simultaneously reduce oxidative damage and increase antioxidant contents of plants and that the accumulation of antioxidants would be a consequence of the endophyte ability to regulate the expression of plant antioxidant genes. We investigated the effects of the fungal endophyte Epichloë gansuensis (C.J. Li & Nan) on oxidative damage, antioxidant contents, and expression of representative genes associated with antioxidant pathways in Achnatherum inebrians (Hance) Keng plants subjected to low (15%) and high (60%) soil moisture conditions. Gene expression levels were measured using RNA-seq. As expected, the endophyte reduced the oxidative damage by 17.55% and increased the antioxidant contents by 53.14% (on average) in plants subjected to low soil moisture. In line with the accumulation of antioxidants in plant tissues, the endophyte increased the expression of most plant genes associated with the biosynthesis of antioxidants (e.g., MIOX, crtB, gpx) while it reduced the expression of plant genes related to the metabolization of antioxidants (e.g., GST, PRODH, ALDH). Our findings suggest that endophyte ability of increasing antioxidant contents in plants may reduce the oxidative damage caused by stresses and that the fungal regulation of plant antioxidants would partly explain the accumulation of these compounds in plant tissues.

The microbiota diversity of Festuca sinensis seeds in Qinghai-Tibet Plateau and their relationship with environments

A total of 14 Festuca sinensis seed lots were collected from different geographical locations on the Qinghai-Tibet Plateau to study the seed microbiota and determine the abiotic (temperature, precipitation, and elevation) and biotic (Epichloë sinensis infection rate) factors likely to shape the seed microbiome. The 14 seed lots had different bacterial and fungal structures and significantly different diversities (p < 0.05). The α-diversity indices of the bacteria were significantly correlated with precipitation (p < 0.05), whereas those of the fungi were significantly correlated with temperature (p < 0.05). Microbiota analysis showed that Proteobacteria, Cyanobacteria, and Bacteroidetes were the most abundant bacteria at the phylum level in the seeds, and Ascomycota and Basidiomycota were the most abundant fungi. β-diversity analysis suggested large differences in the microbial communities of each sample. Redundancy analysis showed that temperature and precipitation were the main environmental factors that drive variations in the microbial community, at the medium-high elevation (3,000–4,500 m), the impact of temperature and precipitation on microbial community is different, and the other elevations that effect on microbial community were basically identical. Spearman's correlation analysis showed that the relative abundances of the most abundant bacterial phyla were significantly correlated with temperature (p < 0.05), whereas those of the most abundant fungal phyla were significantly correlated with precipitation (p < 0.05). E. sinensis infection rates were significantly correlated with elevation and temperature (p < 0.05). These results suggest that temperature and precipitation are the key factors driving the microbial community, that temperature and elevation also had a great influence on the E. sinensis infection rate, and that environmental factors (temperature and elevation) may further affect the microbial community by regulating the E. sinensis infection rate.

Culturable Seed Microbiota of Populus trichocarpa

Plants harbor a diverse community of microbes, whose interactions with their host and each other can influence plant health and fitness. While microbiota in plant vegetative tissues has been extensively studied, less is known about members of the seed microbiota. We used culture-based surveys to identify bacteria and fungi found in the seeds of the model tree, Populus trichocarpa, collected from different sites. We found that individual P. trichocarpa seeds typically contained zero or one microbe, with common taxa including species of Cladosporium, Aureobasidium, Diaporthe, Alternaria, and Pseudomonas, a bacterium. Pseudomonas isolates were associated with seed mortality and were negatively associated with the occurrence of fungal isolates within Epicoccum, Alternaria, and Aureobasidium from the same seed. Next, we conducted an inoculation experiment with one of the isolated seed microbes, Pseudomonas syringae pv. syringae, and found that it reduced seed germination and increased seedling mortality for P. trichocarpa. Our findings highlight common fungi and bacteria in the seeds of P. trichocarpa, prompting further study of their functional consequences. Moreover, our study confirms that P. syringae pv. syringae is a seed pathogen of P. trichocarpa and is the first report that P. syringae pv. syringae is a lethal seedling pathogen of P. trichocarpa, allowing for future work on the pathogenicity of this bacterium in seedlings and potential antagonism with other seed microbes.

An endophytic Talaromyces omanensis enhances reproductive, physiological and anatomical characteristics of drought-stressed tomato

The effects of a newly discovered endophytic fungus, Talaromyces omanensis, on the drought tolerance of tomato is presented in this study. The fungus was obtained from a desert plant Rhazya stricta in Oman. Drought stress was induced by a 15% solution of Polyethylene glycol-6000 (PEG-6000). Several parameters were measured including pollen sterility, pollen tube length, growth, flowering, and yield characteristics, the biochemical analysis of the leaves and fruits, as well as other physiological and anatomical parameters. The results showed that T. omanensis provided multiple advantages to tomato grown under drought stress, including improved reproductive characteristics, chlorophyll fluorescence, and some anatomical characteristics such as increased phloem and cortex width and a reduction of pith autolysis that leads to hollow stem. In addition, T. omanensis significantly increased drought-stress related characteristics such as shoot dry weight, root length, the number of flowers, and fruit weight. A significantly higher concentration of gibberellic acid (GA₃) was found in tomato plants treated by T. omanensis, which may enhance their drought tolerance. These results suggest that T. omanensis is a potential biological anti-stress stimulator for important horticultural crops such as tomatoes. This study is the first to report the beneficial effects of T. omanensis in alleviating drought stress in tomatoes.