Should I fight or should I grow now? The role of cytokinins in plant growth and immunity and in the growth–defence trade-off

Abstract

Background Perception and activation of plant immunity require a remarkable level of signalling plasticity and control. In Arabidopsis and other plant species, constitutive defence activation leads to resistance to a broad spectrum of biotrophic pathogens, but also frequently to stunted growth and reduced seed set. Plant hormones are important integrators of the physiological responses that influence the outcome of plant-pathogen interactions.Scope We review the mechanisms by which the plant hormone cytokinin regulates both plant growth and response to pathogens, and how cytokinins may connect these two processes, ultimately affecting the growth tradeoffs observed in plant immunity.

Role of Cytokinins for Interactions of Plants With Microbial Pathogens and Pest Insects

“…The SA-dependence of CK-induced immunity can support inducing activity of CK, in which exogenous application of CK show increased level of SA-dependent gene expression during pathogen infection (Albrecht and Argueso, 2017). In rice, external application of SA analogue benzothiadiazole Smethylester (BTH) and kinetin rapidly increased expression of defence genes OsPR1b and PBZ1 (see Appendix), while application of either hormone alone did not show a meaningful increase in defence gene expression, nor did cotreatment with SA and several hormones (Jiang et al, 2013;Albrecht and Argueso, 2017).…”

“…Higher level of CK in plant increased resistance to pathogens whereas opposite is true for plant susceptibility to diseases (Choi et al, 2010;Grosskinsky et al, 2011;Naseem et al, 2014;Grosskinsky et al, 2016;Albrecht and Argueso, 2017). Sufficient evidences are available in literature indicating the role of exogenously applied CK on altering the level of host resistance to pathogen (Grosskinsky et al, 2011;Naseem et al, 2014;Grosskinsky et al, 2016;Cortleven et al, 2019).…”

“…Resource allocation in plants for growth and defence needs to be regulated efficiently (Pieterse et al, 2014). Recent findings in plant related researches have indicated that phytohormone signaling networks play role in interconnecting growth, development and defence, making plants to choose when to invest their resource; under favourable condition in growth and development or in defence when they are exposed to biotic or abiotic stresses (Pieterse et al, 2014;Albrecht and Argueso, 2017). Metabolic reprogramming and source to sink ratio of resources could be responsible for growth and development limitation during defence priming (Albrecht and Argueso, 2017), several lines of experimental evidence showed that this kind of scenario may not indicate the full picture of growthdefence trade-offs (Bennett et al, 2012;Giron et al, 2013;Albrecht and Argueso, 2017).…”

Structural and functional insights into the modulation of the activity of a flax cytokinin oxidase by flax rust effector AvrL567‐A

“…Although cytokinins are mainly known for their control of plant cell division, growth and development, more instances of their roles in plant–pathogen interactions are appearing and this is an expanding area of study (Albrecht and Argueso, ; Naseem et al , ). The involvement of increased levels of cytokinins in plant tumour and leafy gall diseases, such as crown gall and witches broom, is well known (Naseem et al , ).…”

Auxins and cytokinins – the dynamic duo of growth‐regulating phytohormones heading for new shores

“…Interestingly, this resistance mechanism appears to be integral to the biocontrol ability of a Pseudomonas fluorescens strain, which induces resistance in the host plant by its bacterial cytokinin production (Großkinsky et al ., ). Thus, cytokinins can prime plant defense responses as highlighted by Cris Argueso (Colorado State University, Fort Collins, CO, USA), and may integrate resistance mechanisms with growth responses in interaction with other phytohormones such as auxin (Albrecht & Argueso, ). The findings of phytohormone production by U. maydis and P. fluorescens as a relevant parameter for their interaction with their host plants was complemented by Megan Aoki (Trent University, Peterborough, Canada) who reported on cytokinin functions in the ameboid slime mould Dictyostelium discoideum .…”