5.1 Introduction
Endophytic microorganisms (bacteria or fungi) are belonging to a key class of plant
symbionts, living inside the plant tissues without causing any symptoms of disease
to the host. These endophytic microorganisms are associated with the plant
throughout their life history, starting from seed germination to fruit development.
These can be distributed in rhizosphere (roots), phylloplane (in leaves), laimosphere
caulosphere (in stems), carposphere (in fruits), spermosphere (in seeds), and an-
thosphere (inflowers) as suggested by Clay and Holah ( 1999 ). Various workers
(Lindow and Brandl 2003 ; Saikkonen et al. 2004 ; Sessitsch et al. 2012 ) stated the
role of endophytes, bacteria, and or fungi unique in their interactions with plants.
They provide an alternative resource or facilitate the distribution or production of
biologically active metabolites, such as enzymes, biofunctional chemicals, phyto-
hormones, nutrient, and minerals (Schulz et al. 2002 ). On the other hand, the host
plant provides a protective sanctuary to reproduce and nutrients to grow inside plant
tissues without compromising its own growth resources (Khan et al. 2015 ).
Endophytic microorganisms have also been coined for their protective role to the
host during biotic and abiotic stress conditions (Arachevaleta et al. 1989 ; Bacon
1993 ; White and Torres 2010 ; Leitão and Enguita 2016 ). These stresses include
salinity, drought, temperature, heavy metal, and phytopathogenic infections. In
most of the previous studies, this role of counteracting stress invasion to the plant
cell has been revoked or reduced through the production of essential biochemical
resources (Khan et al. 2015 ). Among these sources, phytohormones and extracel-
lular enzymes are few which have been regarded the most important and significant
for their association with plants. Though phytohormones are one of the recent
phenomena that have been known from endophytes, however, extracellular
enzymes or exozymes have mostly been emphasized due to their industrial
importance in food, fermentation dye synthesis, and other biotechnological appli-
cations (Traving et al. 2015 ).
Fungi and bacteria produce various kinds of extracellular enzymes, which are
hydrolases, lyasese, oxidoreductases, and transferases (Traving et al. 2015 ). These
extracellular enzymes target various macromolecules such as carbohydrates, lignin,
organic phosphate, proteins, and sugar-based polymers to breakdown into trans-
portable product throughout the cells and to continue heterotopic metabolism
(Sinsabaugh 1994 ; Boer et al. 2005 ; Strong and Claus 2011 ; Wingender et al.
2012 ). Hallmann et al. ( 1997 ) showed that endophyte-producing enzymes could
help to initiate the host symbiosis process. Besides establishment of association
with host, these also initiate action of extracellular hydrolyases to counteract plant
pathogenic infection (Tan and Zou 2001 ; Leo et al. 2016 ). Since, the endophytic
resources offer a new source of genes, enzymes, and secondary metabolites,
therefore, we aimed to investigate in the current chapter broadening our under-
standing related to extracellular enzymes from endophytic origin.
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