Other potential antimicrobial bioactivity metabolites
According to the Green et al. (2020) study on E. festucae -L. perenne symbiont,
Epichloëcyclins
(A-E) were the most abundant class of DMs between symbionts and
non-symbionts. Epichloëcyclins (cyclic peptides) were composed of
lysine, tyrosine, proline, methionine, phenylalanine, and arginine and
might have a bioactive role (Johnson et al. 2015). As epichloëcyclins
information was not obtained in our metabolite database, we did not
detect epichloëcyclins in EI plants in this study. However, endophytes
induced the accumulation of lysine, arginine, and proline, the main
constitutes of epichloëcyclins. Therefore, Epichloëcyclins might occur
in A. sibiricum and possess antimicrobial activities. Moreover,
Aspergillomarasmine A and 4-Methyl-5-thiazoleethanol were highly
accumulated in the endophyte-infected host. Aspergillomarasmine A is a
rapid and effective enzyme inhibitor that restores the sensitivity of
carbapenems to resist bacteria (Meziane-Cherif and Courvalin, 2014).
Thiazoles with fungicidal effects have been widely used in disease
prevention and crops control (Cui et al., 2012). Therefore,
Aspergillomarasmine A and 4-methyl-5-thiazoleethanol might play a role
in the endophyte-associated pathogen resistance of the
host.
In summary, We first reported thatE. sibirica endophytes activated the ISR in the host by JA and ET
signaling pathways which might play an essential role in enhancing host
disease resistance. In addition, we discovered that the antimicrobial
phenolic metabolites and potential bioactive metabolites were
accumulated in large quantities in endophyte-infected
leaves. So far, achievements have
been made in breeding Epichloë -grass symbionts that do not
produce toxic alkaloids to mammals but have toxic alkaloids to insect
herbivores (Bharadwaj et al., 2020).
Once the metabolites responsible
for pathogen resistance are further tested, the endophyte-grass
symbionts will become crucial resources of biological pesticides.