CONCLUSION AND PERSPECTIVES
In conclusion, recent advances confirm that the soil microbiome is key
to soil and plant health, as discussed above. It is perhaps not
surprising that plant-microbe interactions have not been exploited for
agricultural purposes ago, given the relatively poor indicators of
success under field conditions. However, our understanding of the
potential positive effects of PGPM has greatly increased in recent
years, as has our knowledge of underpinning mechanisms, particularly the
molecules involved in inter-organism communication. Thus, while there
are substantial gaps in current knowledge, plant-microbe interactions
are an attractive target for improving crop resilience and for achieving
sustainable yields under unfavourable environmental conditions.
Ultimately, the optimisation of plant-microbe interactions will be
pivotal to strategies aimed at the long-term carbon sequestration in
soils that is crucial to nature-based solutions to climate change.
Microorganisms are at the core of the global carbon cycle, not least
because they are responsible for more than 50% of annual
CO2/methane transformations and contribute to almost
50% of the annual global CO2-sequestration. Engineering
a more sustainable carbon cycle requires a detailed molecular
mechanism-based understanding of the enzymes involved in
CO2/methane interconversions. This essential knowledge
is a prerequisite for viable microbe-based solutions to climate change.
Tailoring the soil microbiome to boost plant yield is currently
restricted to agricultural practices and adding probiotic microbial
consortia, largely because gene editing approaches are limited by
societal acceptance. Ambitious objectives have been set in Europe and in
other continents to ensure food sovereignty, while enhancing
agricultural sustainability. Such targets have to incorporate climate
change reliance traits, together with a much higher efficiency in the
use of essential resources particularly water, and soil nutrients. An
ultimate aim is to reduce reliance on fertilizers and plant protection
products. It will not be possible to achieve these goals without a
revolution in plant breeding that includes a continuous flow of
innovation and technology transfer, incorporating new knowledge as it
becomes available. This requires a substantial acceleration in the
development of new plant varieties that have improved microbial
associations, and so can use available resources much more efficiently,
and are better adapted to climate change. The rapid introduction of such
varieties will only be possible if breeders have access to all of the
available tools and technologies, and crucially that Government
registration and legislation accepts new genomic technologies that are
at the heart of current accelerated breeding opportunities.
Nano-enabled approaches have the potential to overcome the limitations
of traditional microbiome engineering, such as the absence of
specificity in attaining targeted manipulation, collateral fatality to
microbial diversity, and lack of reliable robust results (Fig. 4E)
(Hussain et al., 2023; You, Kerner, Shanmugam, & Khodakovskaya, 2023).
However, the application of novel nanomaterials still requires
comprehensive profiling to evaluate long-term efficacy on plant
productivity and ecosystem health (Ahmed, Noman, Gardea-Torresdey,
White, & Li, 2023). To date, the beneficial actions of such approaches
have been studied largely under controlled conditions and hence
effective translation into the field is uncertain. The practical
relevance of increasing mechanistic knowledge hence requires extensive
study under field conditions, where environmental constraints influence
to composition and effectiveness of plant/microbiome interactions. Such
information is essential to understand how we might best apply
inoculants to fields, which remains a significant challenge (Kaminsky et
al. 2018). Nevertheless, the strategies discussed above have as yet
untapped potential, and are particularly important in developing
countries (Ashwathi, 2019).
Soil microbial communities are not constant and vary according to
developmental stage, tissue type, and sampling time (Quiza et al.,
2023). Our increasing knowledge of the leaf and root microbiomes has
demonstrated the diversity of bacteria that are adapted for survival on,
as well as within plants. The phyllosphere is a conducive niche for
horizontal gene transfer (HGT) between epiphytic bacterial strains, the
plant surface thus provides a niche for the evolution of new variants.
Gaining a deeper understanding of this dynamic environment for gene
exchange and the emergence of new strains, together with the
exploitation of the remarkable genomic diversity within epiphytic
populations, will help overcome current limitations in host-range
specificity and allow potential jumping to other host plants. This
together, with a better understanding of the plethora of signalling
molecules including ROS (and associated redox post-translational
modifications) that contribute to the dialogue between plants and
microbes, will provide an improved road map for exploitation of the
bi/tri/multi-partite interactions with beneficial microbes that will
underpin sustainable next-generation agriculture.