The plant endosphere world – bacterial life within plants

Abstract

The plant endosphere is colonized by complex microbial communities and microorganisms, which colonize the plant interior at least part of their lifetime and are termed endophytes. Their functions range from mutualism to pathogenicity. All plant organs and tissues are generally colonized by bacterial endophytes and their diversity and composition depend on the plant, the plant organ and its physiological conditions, the plant growth stage as well as on the environment. Plant-associated microorganisms, and in particular endophytes, have lately received high attention, because of the increasing awareness of the importance of host-associated microbiota for the functioning and performance of their host. Some endophyte functions are known from mostly lab assays, genome prediction and few metagenome analyses; however, we have limited understanding on in planta activities, particularly considering the diversity of micro-environments and the dynamics of conditions. In our review, we present recent findings on endosphere environments, their physiological conditions and endophyte colonization. Furthermore, we discuss microbial functions, the interaction between endophytes and plants as well as methodological limitations of endophyte research. We also provide an outlook on needs of future research to improve our understanding on the role of microbiota colonizing the endosphere on plant traits and ecosystem functioning.

The soil crisis: the need to treat as a global health problem and the pivotal role of microbes in prophylaxis and therapy

“…10 7 microbes per g of root, 10 3 À10 4 per g leaves, and 10 2 per g of seeds or flowers (e.g. Abdelfattah et al, 2021;Compant et al, 2021). Different plants recruit different microbes, thereby assembling a wide diversity of holobiont compositions that provide considerable capacity for adaptation-evolution of the holobiont to changing environmental conditions and stresses, and for exploration of new habitats to colonize (de Zelicourt et al, 2013).…”

“…Another well-studied example of chemical connectivity is signalling. Plants deposit 10-40% of the photosynthetically fixed carbon via their root system in soil (Compant et al, 2021). As a consequence, the microbial density in the rhizosphere is 10-fold to 100-fold higher than surrounding soil and the composition of its microbial community is distinct from that of the surrounding bulk soil, a phenomenon called the rhizosphere effect (Walters et al, 2018;Kong, et al, 2019).…”

Revisiting Plant–Microbe Interactions and Microbial Consortia Application for Enhancing Sustainable Agriculture: A Review

“…Unique environments for endophytic and epiphytic microbial diversities have been provided by different aboveground plant tissues such as vegetative foliar tissues, leaves, and floral parts, but the major differences in ecology of endospheric (endosphere is inside the environment of plant where microbes survive and may or may not be harmful to the plants; Hardoim et al, 2015 ; Compant et al, 2020 ) and phyllospheric (phyllosphere refers to the aerial region of the plant colonized by microbes) bacterial diversity exist. Systematic distribution of endophytes to different compartments such as stem, leaves, and fruits is facilitated by xylem ( Compant et al, 2010 ), but it is observed that their entry to plant tissues can also take place through aerial parts such as fruits and flowers ( Compant et al, 2011 ).…”

Bacterial endophytes: Molecular interactions with their hosts

“…Endophytic bacteria living inside plants without causing apparent disease symptoms are known for more than 70 years [1,2]. Since then, a large number of Gram‐positive and Gram‐negative bacteria from the most diverse genera Acidobacterium, Alcaligenes, Azoarcus, Azospirillum, Bacillus, Burkholderia, Corynebacterium, Curtobacterium, Enterobacter, Gluconoacetobacter, Herbaspirillum, Klebsiella, Kosakonia, Methylobacterium, Microbacterium, Nocardioides, Pantoea, Paenibacillus, Pseudomonas, Rhanella, Rhizobium, Sphingomonas, Stenotrophomonas, Streptomyces , and Verrucomicrobium have been reported as endophytes [3–6]. The biological role of bacterial endophytes in many plants, however, is still not completely understood.…”