Research

Hormonal Crosstalk in Plant Growth and Immunity

Plant hormones regulate several aspects of plant development and responses to the environment, including responses to pathogens. The complex network of communication among plant hormone signaling pathways is often referred to as hormonal crosstalk. Such interplay among different hormonal pathways allow for the concomitant regulation of different hormone-regulated physiological processes, helping plants fine-tune growth, development and responses to biotic and abiotic stresses. 

 

In our lab we use plant genetics, transcriptomics, mass spectrometry-based high-throughput hormone quantification and mathematical modeling approaches to probe how the different hormonal pathways intersect with each other during growth and immune responses. In the future, our work may lead to the engineering of hormonal crosstalk, to achieve pathogen resistance and increased abiotic tolerance and overall fitness. 

 

Hormonal Regulation of Plant Immunity

Complex hormone crosstalk interactions in response to biotic stress, abiotic stress and during plant growth(a) Interactions between different plant hormone pathways (lines) during plant immunity through shared signaling proteins that may function as potential hormone crosstalk hubs (dark-gray boxes). Purple boxes indicate general hormone classifications. Gray circles represent the major classes of plant hormones. From Shigenaga et al., 2017.

Hormonal regulation of plant immunity

Arabidopsis plants are less susceptible to a biotrophic pathogen if pre-treated with cytokinin. Left: Trypan blue staining of Arabidopsis Col-0 infected with an oomycete pathogen (Hyaloperonospora arabidopsidis). Right: Same as on the left, but plants were treated with cytokinin (benzyl adenine, BA) before pathogen inoculation. Notice less hyphal growth, pathogen sporulation and occasional triggeering of cell death on the right, compared to the leaf on the left. From Argueso et al., 2012.

For the past four decades, the plant hormones salicylic acid, jasmonic acid and ethylene were considered the main hormones regulating plant immunity. Today we know that, akin to their role in plant development,  all hormones have a role in orchestrating the outcome of plant defense responses against invanding pathogens. In our lab we study how plant hormones regulate responses to pathogens. We focus mostly on the plant hormones salicylic acid and cytokinin, which have been shown to regulate responses to biotrophic pathogens, which are those that obtain their nutrients from living plant cells. Previous work has shown that proteins involved in cytokinin signaling regulate salicylic acid-dependent responses in the plant, in an classic example of hormonal crosstalk in immunity.

 

A model on how cytokinin (CK) and salicylic acid (SA) are believed to contribute to immunity against the oomycete pathogen Hyaloperonospora arabidopsidis (Hpa).  From Argueso et al., 2012.

Using a systems biology type of approach we are mining and modeling transcriptomics, metabolomics and phenotyping data, to identify gene networks that regulate defense responses againts biotrophic pathogens. For this work we take advantage of the amazing genetic resources available for the model plants species Arabidopsis thaliana, and its amenability to model pathogens such as the bacterium Pseudomonas syringae pv. tomato and the oomycete Hyaloperonospora arabidopsidis.  

Hormonal regulation of plant-pathogen-environment interactions

The world climate is changing rapidly, and fast adaptation to the new environmental conditions will  be a challenge for both plants and plant pathogens. The effects of warming trends associated with climate change on plant disease will vary depending on the specific pathosystem, but there is consensus among scientists that changes in temperature and precipitation will increase plant disease severity for many plant species. 

Aside from their role in development and plant immunity, plant hormones also regulate responses to abiotic stress. For example, the plant hormone cytokinin is involved in the regulation of responses to changes in temperature, water availability and osmotic potential.  In our lab, we use a comprehenseive approach to determine the role of plant hormones and hormone-regulated gene networks  in the regulation of simultaneous biotic and abiotic stresses. 

 

The expression of genes encoding cytokinin signaling proteins is regulated by exposure to abiotic stress. From Argueso et al., 2009. 

by Cris Argueso, 2019.