Page 2 Plant-Bacteria Interactions Edited by Iqbal Ahmad, John ...

This appears to be a very promising approach toward preventing AHL signaling in
plant-associated/pathogenic bacteria compared to the GM plant approach.
7.7
Conclusion
It is now clear that QS is a widespread gene-regulatory mechanism among Gramnegativebacteria.However,QSinGram-positivebacteriahasnowbeenexploredinfew
cases. In plant-associated bacteria, including pathogenic ones, a variety of traits are
under QS control. However, many traits are still to be reconfirmed. Extensive informationonthechemicalstructureandfunctionofQSmoleculesamongGram-negative
bacteria is now available. The signal molecules exhibit structural diversity and most
common signal molecules are AHLs. Interestingly, QS has been identified as a novel
target to influence the bacterial virulence and pathogenicity. The natural and synthetic
compounds having QS-interfering properties have been identified. It is conceivable
that quorum-sensing inhibition may represent a natural, widespread, antimicrobial
strategy utilized by plants and other organisms with significant impact on biofilm
formation. The QS may be targeted in different way. The creation of transgenic plants
that express bacterial QS genes is yet another interesting strategy to interfere with
bacterial behavior and disease control. Plants are now known to harbor anti-QS activity/metabolites
that could disrupt the QS-controlled pathogenicity of bacteria and
manipulate plant–microbe interactions to obtain improved crop production. More
fundamental research on this mechanism and the presence of multiple QS systems
and their interaction with each other in a single bacterial species remains to be conducted.
Now, with the advanced understanding of QS systems operating in various
microorganisms and methods for characterization of QS molecules and existence of
bacteria-to-bacteria and bacteria-to-plant interactions, we are able to target QS-regulated
functions by either (i) degrading or inhibiting QS signals, signal–cell receptors.
However, many questions remain to be solved as an in-depth knowledge of the
AHL signaling system, which is common in a number of important plant-associated
bacteria, is needed. It is possible that gross disruption of AHL-based communication
in the rhizosphere may adversely affect the colonization or behavior of a number of
important growth-promoting or biocontrol species [90]. Many more interesting
phenomena between mixed microbial communities and their interactions with
plants are to be explored.
Acknowledgments
Acknowledgmentsj147
We are thankful to Professor Robert J.C. McLean (USA) for his encouragement
and support to work on QS and Professor John Pitchel (USA) and Dr S. Hayat (AMU,
Aligarh) for critical input and preparation of this manuscript. Finally, the cooperation
received by students, especially by Mohd Imran and Miss Sameena Hasan,
(AMU) are thankfully acknowledged.