Functional symbiosis is considered one of the successful mechanisms by which plants that inhabit extreme environment improve their ability to tolerate different types of stress. One of the most conspicuous type of symbiosis is the endophyticism. This interaction has been noted to play a role in the adaptation of the native vascular plant Colobanthus quitensis to the stressful environments of Antarctica, characterized by low temperatures and extreme aridity. Projections of climate change for this ecosystem indicate that abiotic conditions will be less limiting due to an increase in temperature and water availability in the soil. Due to this decrease in stress induced by the climate change, it has been suggested that the positive role of fungal endophytes on performance of C. quitensis plants would decrease. In this study, we evaluated the role of endophytic fungi on osmoprotective molecules (sugar production, proline, oxidative stress) and gene expression (CqNCED1, CqABCG25, and CqRD22) as well as physiological traits (stomatal opening, net photosynthesis, and stomatal conductance) in individuals of C. quitensis. Individual plants of C. quitensis with (E+) and without (E−) endophytic fungi were exposed to simulated conditions of increased water availability (W+), having the current limiting water condition (W−) in Antarctica as control. The results reveal an endophyte-mediated lower oxidative stress, higher production of sugars and proline in plants. In addition, E+ plants showed differential expressions in genes related with drought stress response, which was more evident in W− than in W+. These parameters corresponded with increased physiological mechanisms such as higher net photosynthesis, stomatal opening and conductance under presence of endophytes (E+) as well as the projected water condition (W+) for Antarctica. These results suggest that the presence of fungal endophytes plays a positive role in favoring

No abstract

The different torques applied to the abutment-implant system condition the bacterial leakage at the implant interface. No microleakage was observed at 20 and 30 N.

Antarctic plants have developed mechanisms to deal with one or more adverse factors which allow them to successfully survive such extreme environment. Certain effective mechanisms to face adverse stress factors can arise from the establishment of functional symbiosis with endophytic fungi. In this work, we explored the role of fungal endophytes on host plant performance under high level of UV-B radiation, a harmful factor known to damage structure and function of cell components. In order to unveil the underlying mechanisms, we characterized the expression of genes associated to UV-B photoreception, accumulation of key flavonoids, and physiological responses of Colobanthus quitensis plants with (E+) and without (E−) fungal endophytes, under contrasting levels of UV-B radiation. The deduced proteins of CqUVR8, CqHY5, and CqFLS share the characteristic domains and display high degrees of similarity with other corresponding proteins in plants. Endophyte symbiotic plants showed lower lipid peroxidation and higher photosynthesis efficiency under high UV-B radiation. In comparison with E−, E+ plants showed lower CqUVR8, CqHY5, and CqFLS transcript levels. The content of quercetin, a ROS-scavenger flavonoid, in leaves of E-plants exposed to high UV-B was almost 8-fold higher than that in E+ plants 48 h after treatment. Our results suggest that endophyte fungi minimize cell damage and boost physiological performance in the Antarctic plants increasing the tolerance to UV-B radiation. Fungal endophytes appear as fundamental biological partners for plants to cope with the highly damaging UV-B radiation of Antarctica.

The effects of microorganisms on plant-insect interactions have usually been underestimated. While plant growth-promoting rhizobacteria (PGPR) are known to induce plant defenses, endosymbiotic bacteria hosted by herbivorous insects are often beneficial to the host. Here, we aimed to assess whether PGPR-induced defenses in broad bean plants impact the pea aphid, depending on its genotype and the presence of endosymbionts. We estimated aphid reproduction, quantified defense- and growth-related phytohormones by GC-MS, and measured different plant growth and physiology parameters, after PGPR treatment. In addition, we recorded the feeding behavior of aphids by electropenetrography. We found that the PGPR treatment of broad bean plants reduced the reproduction of one of the pea aphid clones. We highlighted a phenomenon of PGPR-induced plant defense priming, but no noticeable plant growth promotion. The main changes in aphid probing behavior were related to salivation events into phloem sieve elements. We suggest that the endosymbiont Hamiltonella defensa played a key role in plant-insect interactions, possibly helping aphids to counteract plant-induced resistance and allowing them to develop normally on PGPR-treated plants. Our results imply that plant- and aphid-associated microorganisms add greater complexity to the outcomes of aphid-plant interactions.