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Abstract Strigolactones (SLs) are a unique and novel class of phytohormones that regulate numerous processes of growth and development in plants. Besides their endogenous functions as hormones, SLs are exuded by plant roots to stimulate critical interactions with symbiotic fungi but can also be exploited by parasitic plants to trigger their seed germination. In the past decade, since their discovery as phytohormones, rapid progress has been made in understanding the SL biosynthesis and signaling pathway. Of particular interest are the diversification of natural SLs and their exact mode of perception, selectivity, and hydrolysis by their dedicated receptors in plants. Here we provide an overview of the emerging field of SL perception with a focus on the diversity of canonical, non-canonical, and synthetic SL probes. Moreover, this review offers useful structural insights into SL perception, the precise molecular adaptations that define receptor-ligand specificities, and the mechanisms of SL hydrolysis and its attenuation by downstream signaling components.
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Dominant-Negative KAI2d Paralogs Putatively Attenuate Strigolactone Responses in Root Parasitic Plants
Abstract Many root parasitic plants in the Orobanchaceae use host-derived strigolactones (SLs) as germination cues. This adaptation facilitates attachment to a host and is particularly important for the success of obligate parasitic weeds that cause substantial crop losses globally. Parasite seeds sense SLs through ‘divergent’ KARRIKIN INSENSITIVE2 (KAI2d)/HYPOSENSITIVE TO LIGHT α/β-hydrolases that have undergone substantial duplication and diversification in Orobanchaceae genomes. After germination, chemotropic growth of parasite roots toward a SL source also occurs in some species. We investigated which of the seven KAI2d genes found in a facultative hemiparasite, Phtheirospermum japonicum, may enable chemotropic responses to SLs. To do so, we developed a triple mutant Nbd14a,b kai2i line of Nicotiana benthamiana in which SL-induced degradation of SUPPRESSOR OF MORE AXILLARY GROWTH2 (MAX2) 1 (SMAX1), an immediate downstream target of KAI2 signaling, is disrupted. In combination with a transiently expressed, ratiometric reporter of SMAX1 protein abundance, this mutant forms a system for the functional analysis of parasite KAI2d proteins in a plant cellular context. Using this system, we unexpectedly found three PjKAI2d proteins that do not trigger SMAX1 degradation in the presence of SLs. Instead, these PjKAI2d proteins inhibit the perception of low SL concentrations by SL-responsive PjKAI2d in a dominant-negative manner that depends upon an active catalytic triad. Similar dominant-negative KAI2d paralogs were identified in an obligate hemiparasitic weed, Striga hermonthica. These proteins suggest a mechanism for attenuating SL signaling in parasites, which might be used to enhance the perception of shallow SL gradients during root growth toward a host or to restrict germination responses to specific SLs.
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- Award ID(s):
- 1922642
- PAR ID:
- 10561532
- Publisher / Repository:
- Oxford University Press
- Date Published:
- Journal Name:
- Plant And Cell Physiology
- Volume:
- 65
- Issue:
- 12
- ISSN:
- 0032-0781
- Format(s):
- Medium: X Size: p. 1969-1982
- Size(s):
- p. 1969-1982
- Sponsoring Org:
- National Science Foundation
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