Plant endobiome and climate change

Plants host many mutualistic bacteria and fungi inside their living tissues. Termed the endophytes (endo=inside; phyte=plant), these microbes have coevolved with the plant and constitute a plant’s endobiome. The fungal endophyte-plant association evolved about 400 million years ago. The fungal endophyte-plant host interaction encompasses a balanced antagonism with the endophyte showing controlled virulence and the plant restricts the induction of disease by the endophyte. Considering their evolutionarily long and constant association with plants, it is not surprising that fungal endophytes modulate phenotypic plasticity of plant traits and enhance their host plant's tolerance to heat, drought and salinity, metals and insect pests and pathogens. Although the exact mechanism of the fungal endophyte-induced abiotic stress tolerance is not clear, in a few cases they increase their plant host’s antioxidant enzymes including ascorbate peroxidase and catalase which are associated with salt tolerance of plants. Epigenetic modification and alterations in the levels of abscisic acid, jasmonic acid and salicylic acid induced by endophytes aids plants tolerate heat and drought. Similarly, endophytes upregulate many defence genes of their plant hosts thereby enhancing the plant’s tolerance to peat and pathogen attacks stress. The density of colonization of fungal endophytes in a leaf is high enough to cogitate on their contribution to the carbon dioxide pool within a leaf through their respiration. This condition would tilt the RuBP carboxylase enzyme to function more as a carboxylase than as an oxygenase such that the net photosynthesis is increased and photo respiration in is decreased in C3 plants.

With such an overarching influence, it is logical that fungal endophytes would aid in plants’ resilience to the stresses induced by a rapidly changing climate. With their relatively small genomes, short generation times, recombination and sexual reproduction processes, fungi are expected to support higher rates of evolution than plants and therefore adapt more rapidly to climate change. Apart from this, most species of fungal endophytes are generalists and infect plants widely separated in their taxonomy and geographic location. Hence, fungal endophyte isolates exhibiting a favourable trait could be introduced in a crop experiencing stress due to climate change. Similarly, an endophyte isolate exhibiting higher rate of respiration could be inoculated in crops to increase its photosynthetic efficiency thus increasing crop production and reducing carbon dioxide release in to the atmosphere.

Many of the dominant and commonly occurring endophytes could be latent pathogens behaving as non-disease causing commensal but could become pathogenic due to change in the environmental conditions. It is necessary to study if alteration in the climate could be a signal for such a shift in the life style of endophytes. This is critical since their wide host range could result in epidemics. Thus, the fungal endobiome of plants require immediate attention to manage climate change effects on plants.