The mysterious benefactor of the plant: ENDOPHYTES
WHAT are endophytes
As the name indicates ENDO- within and PHYTA- plants, the organisms that live within the plants are called endophytes or endosphere microbiota. The world within the plants is composed of diverse and abundant microbes that comprise endophytic fungi, bacteria, actinomycetes, archaea, etc.
WHERE do these endophytes reside inside the plant
Endophytes are ubiquitous, they colonize both aerial (stem, leaves, flower, seed, etc.) and below-ground (root) parts of plants. Primitively, these endophytes are believed to occupy only intercellular apoplastic regions. However, many researchers have proven that endophytes could also colonize intracellular regions like the periplasmic region (between the cell wall and plasma membrane), around the nucleus, etc.
HOW do they associate with the plants
Plants carry their own set of endophytes that evolved along with their host. Such types of endophytes are called systemic endophytes, which are cocladogenetic and mutualistic in nature. Those sets of endophytes within the plants that fluctuate spatially and temporally with the environment are called non-systemic endophytes. This set of endophytes is either beneficial or detrimental to the plants. Thus, the plant-endophyte association has three different types of symbiosis viz., mutualism (where both plant and endophyte benefited- TRUE ENDOPHYTE), commensalism (endophytes live within the plant but don’t cause any harm- LATENT PATHOGEN) and parasitism (endophytes continuously irritates the plant and causes disease- HARMFUL PATHOGEN).
WHEN does an endophyte switch its lifestyle to a pathogen
A microbe within the plants can have different lifestyles viz., endophytic, latent pathogenic or a pathogenic lifestyle. Switching of lifestyles between beneficial, pathogenic and neutral endophytes mainly hinges upon host genotype, microbial strain and its titer, nutritional requirement and stress condition. However, striking a balance between the nutrients required by an endophyte and the defense system of the plants decides whether a microbe is an endophyte or a parasite. The balanced plant-endophyte interaction can be seen in the matter of mutualism, whereas commensalism and parasitism are the upshots of imbalanced plant-endophyte interaction.
WHO carries endophytes to the next generation
Endophytes can be transmitted from one generation to the next generation by two disparate means viz., vertical and horizontal transmission. Endophytes are transmitted vertically via seeds or vegetative propagules instead horizontally transmitted endophytes use soil or aerial parts of the plants for their dispersal. Systemic endophytes are transmitted vertically or sometimes horizontally contrarily non-systemic endophytes are transmitted horizontally only.
HOW endophytes are beneficial to their hosts
Endophyte shows their proficiency by augmenting plant growth (production of phytohormones viz., gibberellin, auxin, cytokinin, and ethylene) and nutrient availability (phosphorus solubilization, siderophore production, nitrogen fixation, etc.), thus acting as biostimulants and biofertilizers, respectively. However, these endophytes indirectly protect the plants against biotic and abiotic stresses through special mechanisms viz., antibiosis, hyper parasitism, competition, quorum quenching and/or by promoting plant growth and inducing defense within the plants.
WHY do we need to know about endophytes
Although we know about endophytes and their importance in managing plant pathogens, insects and other abiotic stresses, studies on endophytes and their mechanisms in combating the stresses remain elusive. In recent years, endophytes are attaining greater importance because of the hazardous effects caused by chemical pesticides. So, there is an urgent need to study the association of endophytes, their localization within the plants and the interaction between plants-endophyte and endophyte-pathogens/insects. Thus, the beam of light should fall on the multitrophic interaction of endophytes within plants using modern techniques.
Conclusion
Endophytes are wonder microbes that thrive inside plants for at least a part of their lifecycle. They benefit plants by promoting their growth and making them strong to fight against biotic and abiotic stresses. Thus, acts as a top-notch eco-friendly approach for enhancing plant nutrition and a novel way towards integrated plant disease management.