5.5 Other signaling mechanisms
Another key area for future research is small RNAs, which can play
important regulatory roles in plant responses to stress. Work done in
Arabidopsis has indicated microRNAs (miRNA) are involved in response to
phosphate stress, while miRNAs are responsive to cold stress inBrachypodium distachyon (Fujii et al., 2005; Chiou et al., 2006;
Zhang et al., 2009). Gene expression analysis in soybean indicates
miRNAs play a role in mediating drought and fungal stress (soybean rust
fungus) through modulation of regulation of ROS (Kulcheski et al.,
2011). Small interfering RNAs (siRNAs), including nat-siRNAs, have also
been shown to regulate both abiotic and biotic stress responses in
Arabidopsis and rice (Atkinson & Urwin, 2012). Additionally, small RNAs
play a role in plant developmental processes, including flowering time
and fertility (Atkinson & Urwin, 2012), indicating their key role at
the intersection of plant defense and productivity. This indicates small
RNAs would be a viable future area of research to understand plant
responses to combined stresses. Additional pathways of interest for
future work include genes involved in calcium signaling, mitochondrial
functions, vesicle trafficking, apoptosis, as well as pathway regulation
of the hyper-sensitivity response, epigenetic regulation, and the role
of cis -regulatory elements (CREs) (Fujita et al., 2006; Atkinson
& Urwin, 2012; Kissoudis et al., 2014; Nejat & Mantri, 2017; Shigenaga
et al., 2017; Romero-Puertas et al., 2021; Singh et al., 2021; Zarratini
et al., 2021).
ADDRESSING GAPS IN OUR KNOWLEDGE
In addition to the future research targets outlined above, additional
experimental approaches and techniques could be used to enhance our
understanding of crosstalk and trade-offs of plant biotic and abiotic
stress responses imposed by climate change.
I. Experiments in both controlled environments and in the field
that address realistic depictions of future climate. This includes
evaluating regional versus global impacts of specific abiotic and biotic
stress interactions. By assessing climate scenarios that have resolution
at the regional scale, we can more accurately predict the impacts of
future growing conditions on crops of interest (Leisner, 2020), as well
as gain a better understanding of the mechanisms involved in crop
responses to stress combinations at the physiological, molecular, and
genetic level (Rivero et al., 2022). Additionally, knowledge gaps
related to different plant pathosystems should be addressed, to expand
our understanding to specific plant-pathogen interactions under future
climate scenarios.
II. Modeling and predictive tools for decision making. Precision
agriculture is a large field that is focused on using advanced robotics,
image analysis, and mapping technologies to improve a farmer’s ability
to make decisions regarding soil and water supplies in real-time
(Cisternas et al., 2020). This can help make decision support tools
available for stakeholders to manage plant responses to climate change.
We need to increase efforts to utilize the same concepts of precision
agriculture to the management of pathogen infection. This includes
predicting climate change effects on pathogen emergence using artificial
intelligence and giving decision-makers automated analyses of risk to
make educated decisions during the growing season (Garrett et al.,
2022).
III. Interdisciplinary research to tackle complex problems. We
need to take a systems biology approach to gain a complete picture of
how plants interact with their changing environment. This includes
addressing issues of physiological responses of plants to their
environment, how these are linked to changes at the genetic level, and
how these changes at the whole plant level might translate into
ecological impacts in natural or agroecosystems. Additionally, links
between belowground factors (soil composition, rhizosphere interactions)
and the plant microbiome (Hacquard et al., 2022) will be key to
increasing plant health, defense, and productivity under future climate
conditions.
CONCLUSIONS
Plants must adapt and respond to an ever-changing environment. Human
influence has led to increased CO2 in our atmosphere,
warming of our land, and changes in precipitation patterns. These
changes to our global ecosystem will also lead to changes in the
prevalence and virulence of plant pathogens, and plant herbivores. To
ensure sustainable future food production, we must understand the
crosstalk and trade-offs resulting from combined abiotic and biotic
stress impacts on plant growth and defense. Outcomes from experiments
where plants are exposed to multiple stresses are often unique from the
individual stress alone, especially at the level of gene expression.
There is, however, significant crosstalk among these stresses, with key
hubs of integration of signals across stresses involving transcription
factors, hormones (ABA, SA, JA), ROS, small RNAs, and MAPK cascades.
These are key targets for future research efforts. More combinatorial
stress work is needed in the future to understand growth and defense
trade-offs and crosstalk among plant biotic and abiotic stress
responses. This work should incorporate realistic depictions of future
climate, leverage interdisciplinary teams of researchers, and employ
advanced tools in precision agriculture and predictive tools for
decision making (Fig. 1 ).