Khosla A

References (5)

Title : KARRIKIN UP-REGULATED F-BOX 1 (KUF1) imposes negative feedback regulation of karrikin and KAI2 ligand metabolism in Arabidopsis thaliana - Sepulveda_2022_Proc.Natl.Acad.Sci.U.S.A_119_e2112820119
Author(s) : Sepulveda C , Guzman MA , Li Q , Villaecija-Aguilar JA , Martinez SE , Kamran M , Khosla A , Liu W , Gendron JM , Gutjahr C , Waters MT , Nelson DC
Ref : Proc Natl Acad Sci U S A , 119 :e2112820119 , 2022
Abstract : Significance: Karrikins are chemicals in smoke that stimulate regrowth of many plants after fire. However, karrikin responses are not limited to species from fire-prone environments and can affect growth after germination. Putatively, this is because karrikins mimic an unknown signal in plants, KAI2 ligand (KL). Karrikins likely require modification in plants to become bioactive. We identify a gene, KUF1, that appears to negatively regulate biosynthesis of KL and metabolism of a specific karrikin. KUF1 expression increases in response to karrikin or KL signaling, thus forming a negative feedback loop that limits further activation of the signaling pathway. This discovery will advance understanding of how karrikins are perceived and how smoke-activated germination evolved. It will also aid identification of the elusive KL.
ESTHER : Sepulveda_2022_Proc.Natl.Acad.Sci.U.S.A_119_e2112820119
PubMedSearch : Sepulveda_2022_Proc.Natl.Acad.Sci.U.S.A_119_e2112820119
PubMedID: 35254909

Title : Rapid analysis of strigolactone receptor activity in a Nicotiana benthamiana dwarf14 mutant - White_2022_Plant.Direct_6_e389
Author(s) : White ARF , Mendez JA , Khosla A , Nelson DC
Ref : Plant Direct , 6 :e389 , 2022
Abstract : DWARF14 (D14) is an /beta-hydrolase and receptor for the plant hormone strigolactone (SL) in angiosperms. Upon SL perception, D14 works with MORE AXILLARY GROWTH2 (MAX2) to trigger polyubiquitination and degradation of DWARF53(D53)-type proteins in the SUPPRESSOR OF MAX2 1-LIKE (SMXL) family. We used CRISPR-Cas9 to generate knockout alleles of the two homoeologous D14 genes in the Nicotiana benthamiana genome. The Nbd14a,b double mutant had several phenotypes that are consistent with the loss of SL perception in other plants, including increased axillary bud outgrowth, reduced height, shortened petioles, and smaller leaves. A ratiometric fluorescent reporter system was used to monitor degradation of SMXL7 from Arabidopsis thaliana (AtSMXL7) after transient expression in N. benthamiana and treatment with the strigolactone analog GR24. AtSMXL7 was degraded after treatment with GR24(5DS), which has the stereochemical configuration of natural SLs, as well as its enantiomer GR24 (ent-5DS). In Nbd14a,b leaves, AtSMXL7 abundance was unaffected by rac-GR24 or either GR24 stereoisomer. Transient coexpression of AtD14 with the AtSMXL7 reporter in Nbd14a,b restored the degradation response to rac-GR24, but required an active catalytic triad. We used this platform to evaluate the ability of several AtD14 mutants that had not been characterized in plants to target AtSMXL7 for degradation.
ESTHER : White_2022_Plant.Direct_6_e389
PubMedSearch : White_2022_Plant.Direct_6_e389
PubMedID: 35355884

Title : The strigolactone receptor D14 targets SMAX1 for degradation in response to GR24 treatment and osmotic stress - Li_2022_Plant.Commun_3_100303
Author(s) : Li Q , Martin-Fontecha ES , Khosla A , White ARF , Chang S , Cubas P , Nelson DC
Ref : Plant Commun , 3 :100303 , 2022
Abstract : The effects of the phytohormone strigolactone (SL) and smoke-derived karrikins (KARs) on plants are generally distinct, despite the fact that they are perceived through very similar mechanisms. The homologous receptors DWARF14 (D14) and KARRIKIN-INSENSITIVE2 (KAI2), together with the F-box protein MORE AXILLARY GROWTH2 (MAX2), mediate SL and KAR responses, respectively, by targeting different SMAX1-LIKE (SMXL) family proteins for degradation. These mechanisms are putatively well-insulated, with D14-MAX2 targeting SMXL6, SMXL7, and SMXL8sand KAI2-MAX2 targeting SMAX1 and SMXL2 in Arabidopsis thaliana. Recent evidence challenges this model. We investigated whether D14 can target SMAX1 and whether this occurs naturally. Genetic analysis indicates that the SL analog GR24 promotes D14-SMAX1 crosstalk. Although D14 shows weaker interactions with SMAX1 than with SMXL2 or SMXL7, D14 mediates GR24-induced degradation of SMAX1 in plants. Osmotic stress triggers SMAX1 degradation, which is protective, through SL biosynthesis and signaling genes. Thus, D14-SMAX1 crosstalk may be beneficial and not simply a vestige of the evolution of the SL pathway.
ESTHER : Li_2022_Plant.Commun_3_100303
PubMedSearch : Li_2022_Plant.Commun_3_100303
PubMedID: 35529949

Title : Desmethyl butenolides are optimal ligands for karrikin receptor proteins - Yao_2021_New.Phytol__
Author(s) : Yao J , Scaffidi A , Meng Y , Melville KT , Komatsu A , Khosla A , Nelson DC , Kyozuka J , Flematti GR , Waters MT
Ref : New Phytol , : , 2021
Abstract : Strigolactones and karrikins are butenolide molecules that regulate plant growth. They are perceived via the alpha/beta-hydrolase DWARF14 (D14) and its homologue KARRIKIN INSENSITIVE2 (KAI2), respectively. Plant-derived strigolactones have a butenolide ring with a methyl group that is essential for bioactivity. By contrast, karrikins are abiotic in origin, and the butenolide methyl group is non-essential. KAI2 is probably a receptor for an endogenous butenolide, but the identity of this compound remains unknown. Here we characterise the specificity of KAI2 towards differing butenolide ligands using genetic and biochemical approaches. We find that KAI2 proteins from multiple species are most sensitive to desmethyl butenolides that lack a methyl group. Desmethyl-GR24 and desmethyl-CN-debranone are active via KAI2 but not D14. They are more potent KAI2 agonists than their methyl-substituted reference compounds both in vitro and in plants. The preference of KAI2 for desmethyl butenolides is conserved in Selaginella moellendorffii and Marchantia polymorpha, suggesting that it is an ancient trait in land plant evolution. Our findings provide insight into the mechanistic basis for differential ligand perception by KAI2 and D14, and support the view that the endogenous substrates for KAI2 and D14 have distinct chemical structures and biosynthetic origins.
ESTHER : Yao_2021_New.Phytol__
PubMedSearch : Yao_2021_New.Phytol__
PubMedID: 33474738
Gene_locus related to this paper: arath-AtD14 , arath-KAI2.D14L

Title : Structure-Function Analysis of SMAX1 Reveals Domains That Mediate Its Karrikin-Induced Proteolysis and Interaction with the Receptor KAI2 - Khosla_2020_Plant.Cell_32_2639
Author(s) : Khosla A , Morffy N , Li Q , Faure L , Chang SH , Yao J , Zheng J , Cai ML , Stanga J , Flematti GR , Waters MT , Nelson DC
Ref : Plant Cell , 32 :2639 , 2020
Abstract : Karrikins (KARs) are butenolides found in smoke that can influence germination and seedling development of many plants. The KAR signaling mechanism is hypothesized to be very similar to that of the plant hormone strigolactone (SL). Both pathways require the F-box protein MORE AXILLARY GROWTH2 (MAX2), and other core signaling components have shared ancestry. Putatively, KAR activates the receptor KARRIKIN INSENSITIVE2 (KAI2), triggering its association with the E3 ubiquitin ligase complex SCF(MAX2) and downstream targets SUPPRESSOR OF MAX2 1 (SMAX1) and SMAX1-LIKE2 (SMXL2). Polyubiquitination and proteolysis of SMAX1 and SMXL2 then enable growth responses to KAR. However, many of the assumptions of this model have not been demonstrated. Therefore, we investigated the posttranslational regulation of SMAX1 from the model plant Arabidopsis (Arabidopsis thaliana). We find evidence that SMAX1 is degraded by KAI2-SCF(MAX2) but is also subject to MAX2-independent turnover. We identify SMAX1 domains that are responsible for its nuclear localization, KAR-induced degradation, association with KAI2, and ability to interact with other SMXL proteins. KAI2 undergoes MAX2-independent degradation after KAR treatment, which we propose results from its association with SMAX1 and SMXL2. Finally, we discover an SMXL domain that mediates receptor-target interaction preferences in KAR and SL signaling, laying the foundation for understanding how these highly similar pathways evolved to fulfill different roles.
ESTHER : Khosla_2020_Plant.Cell_32_2639
PubMedSearch : Khosla_2020_Plant.Cell_32_2639
PubMedID: 32434855