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ABSTRACT Plant immunity activation often results in suppression of plant growth, particularly in the case of constitutive immune activation. We discovered that signaling of the phytohormone cytokinin (CK), known to regulate plant growth through the control of cell division and shoot apical meristem (SAM) activity, can be suppressed by negative crosstalk with the defense phytohormones jasmonic acid (JA), and most evidently, salicylic acid (SA). We show that changing the negative crosstalk of SA on CK signaling in autoimmunity mutants by targeted increase of endogenous CK levels results in plants resistant to pathogens from diverse lifestyles, and relieves suppression of reproductive growth. Moreover, such changes in crosstalk result in a novel reproductive growth phenotype, suggesting a role for defense phytohormones in the SAM, likely through regulation of nitrogen response and cellular redox status. Our data suggest that targeted phytohormone crosstalk engineering can be used to achieve increased reproductive growth and pathogen resistance. SIGNIFICANCE STATEMENTPlants constantly integrate environmental stimuli with developmental programs to optimize their growth and fitness. Excessive activation of the plant immune system often leads to decreased plant growth, a process known as the growth-defense tradeoff. Here, we adapted phytohormone levels in Arabidopsis reproductive tissues of autoimmunity mutants to change phytohormonal crosstalk and diminish the growth tradeoff, resulting in increased broad resistance to pathogens and decreased growth suppression. Similar approaches to phytohormone crosstalk engineering could be used in different contexts to achieve outcomes of higher plant stress resilience and yield.
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An emerging signaling hub: KAI2 at the nexus of phytohormone networks
SUMMARY The KARRIKIN INSENSITIVE 2 (KAI2) receptor, originally characterized for its role in seed germination and light‐responsive development, is now recognized as an important signaling component with broad physiological relevance across plant species. While KAI2 is perhaps best known for perceiving exogenous smoked‐derived karrikins, recent discoveries have revealed extensive crosstalk between KAI2‐mediated signaling and multiple phytohormone pathways. We synthesize the current knowledge of KAI2 crosstalk with core plant hormones like strigolactones, auxin, ethylene, gibberellins, abscisic acid, cytokinins, and salicylic acid. We highlight shared signaling components, transcriptional regulation, and physiological outcomes. We examine how KAI2 signaling modulates hormone signaling and discuss the emerging view of KAI2 as an integrator of environmental and hormonal cues, particularly in stress adaptation and developmental plasticity. Finally, we propose new approaches, including proximity‐labeling screens to dissect KAI2's full signaling potential and to explore open questions surrounding the identity and regulation of the endogenous putative KAI2 ligand. These insights position KAI2 as an evolving hub in the plant‐signaling network, with implications for both fundamental research and crop improvement.
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- PAR ID:
- 10661217
- Publisher / Repository:
- The Plant Journal
- Date Published:
- Journal Name:
- The Plant Journal
- Volume:
- 124
- Issue:
- 5
- ISSN:
- 0960-7412
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1111/tpj.70609
