Volatile communication in plants relies on a KAI2-mediated signaling pathway
Ontology highlight
ABSTRACT: Plants are targets of volatile organic compounds (VOCs) released as a part of plant-plant communication, within-plant self-signaling and plant-microbe interactions. Therefore, understanding VOC perception and downstream signaling is vital for unraveling the mechanisms behind information exchange in plants, which remain largely unexplored. Using the hormone-like function of volatile terpenoids in reproductive organ development as a system with a visual marker for communication, we demonstrated that among the four petunia karrikin-insensitive receptors, PhKAI2ia stereo-specifically perceives the (-)-germacrene D signal, triggering a karrikin-like signaling cascade. This study provides new insights into plant olfaction, uncovers the role(s) of the unique intermediate clade of KAI2 receptors, illuminates the involvement of KAI2ia-dependent signaling pathway in volatile communication and gives insight into the long-standing question about the nature of potential endogenous karrikin-like ligand(s).
Project description:In this study, we investigated the potential role of the karrikin receptor KARRIKIN INSENSITIVE2 (KAI2) in the response of Arabidopsis seedlings to high temperature stress.
Project description:Objective: to compare and contrast the effects of exogenous application of karrikins KAR1 and KAR2, and the strigolatone analogue rac-GR24, on gene expression in shoot tissue of seedlings of Brachpodium distachyon (false brome). The experiment compared the effects on three genotypes: wild type Bd21-3, and two mutant alleles for the Brachypodium orthoologue of the karrikin receptor KARRIKIN INSENSITIVE2 (KAI2; Bradi1g15880.1). These alleles were designated Bdkai2-1 and Bdkai2-2.
Project description:The F-box protein MORE AXILLARY GROWTH 2 (MAX2) is a central component in the signaling cascade of strigolactones (SLs) as well as of the smoke derived karrikins (KARs) and the so far unknown endogenous KAI2 ligand (KL). The two groups of molecules are involved in overlapping and unique developmental processes, and signal-specific outcomes are attributed to perception by the paralogous α/β-hydrolases DWARF14 (D14) for SL and KARRIKIN INSENSITIVE 2/ HYPOSENSITIVE TO LIGHT (KAI2/HTL) for KAR/KL. Additionally, depending on which receptor is activated, specific members of the SUPPRESSOR OF MAX2 1 (SMAX1) – LIKE (SMXL) 6, 7, 8 clade control KAR/KL and SL responses respectively. As proteins that function in the same signal transduction pathway often occur in large protein complexes, we aimed at discovering new players of the MAX2, D14 and KAI2 protein network by tandem affinity purification using Arabidopsis cell cultures. When using MAX2 as a bait, various proteins were co-purified among which general components of the Skp1-Cullin-F-box complex and members of the CONSTITUTIVE PHOTOMORPHOGENIC 9 signalosome. Here, we report the identification of a novel interactor of MAX2, a type 5 serine/threonine protein phosphatase, designated PHYTOCHROME-ASSOCIATED PROTEIN PHOSPHATASE 5 (PAPP5). Quantitative affinity purification pointed at PAPP5 as being more present in KAI2 rather than D14 protein complexes. In agreement, mutant analysis suggests that PAPP5 modulates KAR/KL-dependent seed germination in suboptimal conditions and seedling development. Additionally, PAPP5 was found to dephosphorylate MAX2 in vivo independent of the synthetic strigolactone analog, rac-GR24. Together, by analyzing the protein complexes to which MAX2, D14 and KAI2 belong, we revealed a new MAX2 interactor that might act through dephosphorylating MAX2 to control mainly KAR/KL signaling.
Project description:Germination of seeds of Orobanche species requires specific chemicals exuded by host roots. A family of “divergent” KARRIKIN INSENSITIVE2 (KAI2d) genes encode proteins that recognize strigolactone (SL) class germination simulants. We explored specificity of germination stimulant detection by analyzing interspecific segregants of a cross between Orobanche cernua and O. cumana, closely related species that differ in stimulant response. O. cernua parasitizes tomato and germinates in response to the SL orobanchol, while O. cumana parasitizes sunflower and responds to dehydrocostus lactone (DCL). KAI2d genes were catalogued in parents and in segregants that showed stimulant specificity. KAI2d genes were also functionally assayed in the Arabidopsis kai2 mutant background. We identified five full-length KAI2d genes in O. cernua and eight in O. cumana. The O. cernua KAI2d2, as well as its ortholog in O. cumana, are associated with SL perception. A cluster of O. cumana KAI2d genes was genetically linked to DCL perception, although no specific receptor gene was identified by heterologous complementation. These findings support the KAI2d-mediated perception of SLs, but fall short of explaining how O. cumana perceives DCL. The ability of some O. cumana KAI2d genes to detect SLs points to the involvement of additional factors in regulating stimulant specificity.
Project description:To understand the combined role of SL and KAR signaling pathways in regulating levels and metabolism of other plant hormones, we performed the compare transcriptome profiling d14 kai2 and WT plants. Aligent´s whole Arabidopsis Gene Expression Microarray (G2519F-021169, V4, 4x44K) was used.
Project description:Elucidating direct roles of natural variation in biological processes has been challenging due to the difficulty in dissecting the causal role of a gene in traits displaying continuous variation. The decision of a seed to germinate is an easily quantifiable binary choice, which makes it an ideal phenotype to assess the contribution of natural variation in adaptation of plants to begin their lifecycle under optimal conditions. seeds must integrate a complex array of environmental signals to begin their lifecycle under optimal conditions. Light availability is a crucial environmental stimulus that promotes germination in many small seed plant species including Arabidopsis thaliana. Upon perception of light by photoreceptors, phytohormones act as internal signals to coordinate germination but the karrikin (KAR) signalling pathway through the HTL/KAI2 receptor is thought to play a rudimentary role in Arabidopsis germination (REF). Here we show that the AtHTL/KAI2 pathway is required and sufficient to promote germination under low light conditions. Activation of the AtHTL/KAI2 receptor by nanomolar Karrikin2 (KAR2) concentrations or inactivation of SMAX1 bypass the light requirement for germination. By performing a screen of A. thaliana accessions that can germinate under low light conditions, we identified an accession from Afghanistan (Ara-1) which misexpressed AtKAI2/HTL and had a nearly identical transcriptional signature to the activation of AtKAI2 upon addition of KAR2 in the reference accession. Our data suggest that AtKAI2 is a central regulator of germination in natural Arabidopsis populations in response to light availability, to optimize germination timing in their ecological niche.
Project description:In terrestrial ecosystems plants take up phosphate predominantly via association with arbuscular mycorrhizal fungi (AMF). We discovered that the loss of responsiveness to AMF in the rice deletion mutant hebiba is encoded by the alpha/beta fold hydrolase, DWARF 14 LIKE (D14L), which is one of the 26 deleted genes. It is a component of an intracellular receptor complex involved in the detection of the smoke-compound karrikin. On the basis of the early and pronounced hebiba mutant phenotype, we hypothesized that functional D14L is required for the perception of AM fungi prior to contact. Germinated spore exudates of AMF activate pre-contact plant responses. Therefore, we used RNAseq to monitor the transcriptional changes of hebiba and wild type roots in response to germinated spore exudates, and also karrikin, over the first 24 hours post treatment. WT seedlings were treated with GSE, Karrikin or a mock and iho seedlings with GSE or a mock. Root material was collected for sequencing at 0, 3, 6, 9, 12 and 24 hours. This gave a total of 27 samples (WT+Mock: 6, WT+GSE: 5, WT+Karrikin:5, iho+Mock:6, iho+GSE: 5).
Project description:Methyl jasmonate (MeJA) is a well-known plant hormone known for plant defense and plant-plant signaling. However, most of the studies are focussed on its aboveground presence and functions. Here we report that MeJA is also released by plant roots in a volatile form. More importantly, it is shown in Arabidopsis growing in natural conditions in soil.
Project description:Plants perceive herbivory induced volatiles and respond to them by upregulating their defenses. So far, the organs responsible for volatile perception remain poorly described. Here, we show that responsiveness to the herbivory induced green leaf volatile (Z)-3-hexenyl acetate (HAC) in terms of volatile emission, transcriptional regulation and jasmonate defense hormone activation is largely constrained to younger maize leaves. Older leaves are much less sensitive to HAC. In a given leaf, responsiveness to HAC is high at immature developmental stages and drops off rapidly during maturation. Responsiveness to the non-volatile elicitor ZmPep3 shows an opposite pattern, demonstrating that this form of hyposmia (i.e. decreased sense of smell) is not due to a general defect in jasmonate defense signaling in mature leaves. Neither stomatal conductance nor leaf cuticle composition explain the unresponsiveness of older leaves to HAC, suggesting perception mechanisms upstream of jasmonate signaling as driving factors. Finally, we show that hyposmia in older leaves is not restricted to HAC, and extends to the full blend of herbivory induced volatiles. In conclusion, our work identifies immature maize leaves as dominant stress volatile sensing organs. The tight spatiotemporal control of volatile perception may facilitate within-plant defense signaling to protect young leaves, and may allow plants with complex architectures to explore the dynamic odor landscapes at the outer periphery of their shoots