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Salicylic acid (SA) is an important plant hormone with a critical role in plant defense against pathogen infection. Despite extensive research over the past 30 year or so, SA biosynthesis and its complex roles in plant defense are still not fully understood. Even though earlier biochemical studies suggested that plants synthesize SA from cinnamate produced by phenylalanine ammonia lyase (PAL), genetic analysis has indicated that in Arabidopsis, the bulk of SA is synthesized from isochorismate (IC) produced by IC synthase (ICS). Recent studies have further established the enzymes responsible for the conversion of IC to SA in Arabidopsis. However, it remains unclear whether other plants also rely on the ICS pathway for SA biosynthesis. SA induces defense genes against biotrophic pathogens, but represses genes involved in growth for balancing defense and growth to a great extent through crosstalk with the growth-promoting plant hormone auxin. Important progress has been made recently in understanding how SA attenuates plant growth by regulating the biosynthesis, transport, and signaling of auxin. In this review, we summarize recent progress in the biosynthesis and the broad roles of SA in regulating plant growth during defense responses. Further understanding of SA production and its regulation of both defense and growth will be critical for developing better knowledge to improve the disease resistance and fitness of crops.
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CONCERTED PLANT GROWTH AND DEFENSE THROUGH TARGETED PHYTOHORMONE CROSSTALK MODIFICATION
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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- Award ID(s):
- 1818211
- PAR ID:
- 10541040
- Publisher / Repository:
- bioRxiv
- Date Published:
- Format(s):
- Medium: X
- Institution:
- bioRxiv
- Sponsoring Org:
- National Science Foundation
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- https://doi.org/10.1101/2024.04.08.588615
