title: SMAX1-LIKE/D53 Family Members Enable Distinct MAX2-Dependent Responses to Strigolactones and Karrikins in Arabidopsis.
abstract: The plant hormones strigolactones and smoke-derived karrikins are butenolide signals that control distinct aspects of plant development. Perception of both molecules in Arabidopsis thaliana requires the F-box protein MORE AXILLARY GROWTH2 (MAX2). Recent studies suggest that the homologous SUPPRESSOR OF MAX2 1 (SMAX1) in Arabidopsis and DWARF53 (D53) in rice (Oryza sativa) are downstream targets of MAX2. Through an extensive analysis of loss-of-function mutants, we demonstrate that the Arabidopsis SMAX1-LIKE genes SMXL6, SMXL7, and SMXL8 are co-orthologs of rice D53 that promote shoot branching. SMXL7 is degraded rapidly after treatment with the synthetic strigolactone mixture rac-GR24. Like D53, SMXL7 degradation is MAX2- and D14-dependent and can be prevented by deletion of a putative P-loop. Loss of SMXL6,7,8 suppresses several other strigolactone-related phenotypes in max2, including increased auxin transport and PIN1 accumulation, and increased lateral root density. Although only SMAX1 regulates germination and hypocotyl elongation, SMAX1 and SMXL6,7,8 have complementary roles in the control of leaf morphology. Our data indicate that SMAX1 and SMXL6,7,8 repress karrikin and strigolactone signaling, respectively, and suggest that all MAX2-dependent growth effects are mediated by degradation of SMAX1/SMXL proteins. We propose that functional diversification within the SMXL family enabled responses to different butenolide signals through a shared regulatory mechanism.
authors.affiliation: Department of Genetics, University of Georgia, Athens, Georgia 30602.
authors.forename: Ishwarya
authors.identifier: http://orcid.org/0000-0002-3302-6341
authors.initials: I
authors.lastname: Soundappan
authors.affiliation: Sainsbury Laboratory, Cambridge University, Cambridge CB2 1LR, United Kingdom.
authors.forename: Tom
authors.identifier: http://orcid.org/0000-0003-1612-4019
authors.initials: T
authors.lastname: Bennett
authors.affiliation: Department of Genetics, University of Georgia, Athens, Georgia 30602.
authors.forename: Nicholas
authors.identifier: http://orcid.org/0000-0003-3170-2032
authors.initials: N
authors.lastname: Morffy
authors.affiliation: Sainsbury Laboratory, Cambridge University, Cambridge CB2 1LR, United Kingdom.
authors.forename: Yueyang
authors.identifier: http://orcid.org/0000-0002-7427-1028
authors.initials: Y
authors.lastname: Liang
authors.affiliation: Department of Genetics, University of Georgia, Athens, Georgia 30602.
authors.forename: John P
authors.identifier: http://orcid.org/0000-0003-3629-9932
authors.initials: JP
authors.lastname: Stanga
authors.affiliation: Department of Genetics, University of Georgia, Athens, Georgia 30602.
authors.forename: Amena
authors.identifier: http://orcid.org/0000-0002-9049-5232
authors.initials: A
authors.lastname: Abbas
authors.affiliation: Sainsbury Laboratory, Cambridge University, Cambridge CB2 1LR, United Kingdom.
authors.forename: Ottoline
authors.identifier: http://orcid.org/0000-0003-2161-3829
authors.initials: O
authors.lastname: Leyser
authors.affiliation: Department of Genetics, University of Georgia, Athens, Georgia 30602 dcnelson@uga.edu.
authors.forename: David C
authors.identifier: http://orcid.org/0000-0001-9792-5015
authors.initials: DC
authors.lastname: Nelson
mesh_terms: D000483:Alleles; D017360:Arabidopsis / Q000187:drug effects / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000378:metabolism*; D001692:Biological Transport / Q000187:drug effects; D002352:Carrier Proteins / Q000378:metabolism*; D005663:Furans / Q000494:pharmacology*; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D018525:Germination / Q000187:drug effects; D018546:Hypocotyl / Q000187:drug effects / Q000254:growth & development; D007210:Indoleacetic Acids / Q000378:metabolism; D007783:Lactones / Q000494:pharmacology*; D008954:Models, Biological; D005810:Multigene Family; D009154:Mutation / Q000235:genetics; D009928:Organ Specificity / Q000187:drug effects; D018515:Plant Leaves / Q000033:anatomy & histology / Q000187:drug effects; D018517:Plant Roots / Q000187:drug effects / Q000254:growth & development; D018520:Plant Shoots / Q000187:drug effects / Q000254:growth & development; D018547:Plant Stems / Q000187:drug effects / Q000378:metabolism; D011485:Protein Binding / Q000187:drug effects; D059748:Proteolysis / Q000187:drug effects; D011714:Pyrans / Q000494:pharmacology*
chemical_list: C488803:3-methyl-2H-furo(2,3-c)pyran-2-one; D029681:Arabidopsis Proteins; D002352:Carrier Proteins; D005663:Furans; D007210:Indoleacetic Acids; D007783:Lactones; C435920:MAX2 protein, Arabidopsis; D011714:Pyrans