Abstract Karrikins (KARs) are chemicals in smoke that can enhance germination of many plants. Lettuce (Lactuca sativa) cv. Grand Rapids germinates in response to nanomolar karrikinolide (KAR1). Lettuce is much less responsive to KAR2 or a mixture of synthetic strigolactone analogs, rac-GR24. We investigated the molecular basis of selective and sensitive KAR1 perception in lettuce. The lettuce genome contains two copies of KARRIKIN INSENSITIVE2 (KAI2), which in Arabidopsis (Arabidopsis thaliana) encodes a receptor that is required for KAR responses. LsKAI2b is more highly expressed than LsKAI2a in dry achenes and during early stages of imbibition. Through cross-species complementation assays in Arabidopsis, we found that an LsKAI2b transgene confers robust responses to KAR1, but LsKAI2a does not. Therefore, LsKAI2b likely mediates KAR1 responses in lettuce. We compared homology models of KAI2 proteins from lettuce and a fire-follower, whispering bells (Emmenanthe penduliflora). This identified pocket residues 96, 124, 139, and 161 as candidates that influence the ligand specificity of KAI2. Further support for the importance of these residues was found through a broader comparison of pocket residues among 281 KAI2 proteins from 184 asterid species. Almost all KAI2 proteins had either Tyr or Phe identity at position 124. Genes encoding Y124-type KAI2 are more broadly distributed in asterids than in F124-type KAI2. Substitutions at residues 96, 124, 139, and 161 in Arabidopsis KAI2 produced a broad array of responses to KAR1, KAR2, and rac-GR24. This suggests that the diverse ligand preferences observed among KAI2 proteins in plants could have evolved through relatively few mutations.
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Rapid analysis of strigolactone receptor activity in a Nicotiana benthamiana dwarf14 mutant
DWARF14 (D14) is an ɑ/β‐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
- NSF-PAR ID:
- 10364578
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Plant Direct
- Volume:
- 6
- Issue:
- 3
- ISSN:
- 2475-4455
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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R esistance toH eteroderag lycinesRhg1 ) locus to reduce yield losses caused by soybean cyst nematode (SCN).Rhg1 is a tandemly repeated four gene block. Two classes of SCN resistance‐conferringRhg1 haplotypes are recognized:rhg1‐a (“Peking‐type,” low‐copy number, three or fewerRhg1 repeats) andrhg1‐b (“PI 88788‐type,” high‐copy number, four or moreRhg1 repeats). Therhg1‐a andrhg1‐b haplotypes encode α‐SNAP (alpha‐S olubleN SFA ttachmentP rotein) variants α‐SNAPRhg1 LC and α‐SNAPRhg1 HC, respectively, with differing atypical C‐terminal domains, that contribute to SCN resistance. Here we report thatrhg1‐a soybean accessions harbor a copia retrotransposon within theirRhg1 Glyma.18G022500 (α‐SNAP‐encoding) gene. We termed this retrotransposon “RAC, ” forR hg1a lpha‐SNAPc opia. Soybean carries multipleRAC ‐like retrotransposon sequences. TheRhg1 RAC insertion is in theGlyma.18G022500 genes of all truerhg1‐a haplotypes we tested and was not detected in any examinedrhg1‐b orRhg1WT (single‐copy) soybeans.RAC is an intact element residing within intron 1, anti‐sense to therhg1‐a α‐SNAP open reading frame.RAC has intrinsic promoter activities, but overt impacts ofRAC on transgenic α‐SNAPRhg1 LC mRNA and protein abundance were not detected. From the nativerhg1‐a RAC+ genomic context, elevated α‐SNAPRhg1 LC protein abundance was observed in syncytium cells, as was previously observed for α‐SNAPRhg1 HC (whoserhg1‐b does not carryRAC ). Using a SoySNP50K SNP corresponding withRAC presence, just ~42% of USDA accessions bearing previously identifiedrhg1‐a SoySNP50K SNP signatures harbor theRAC insertion. Subsequent analysis of several of these putativerhg1‐a accessions lackingRAC revealed that none encodedα‐SNAPRhg1LC , and thus, they are notrhg1‐a .rhg1‐a haplotypes are of rising interest, withRhg4 , for combating SCN populations that exhibit increased virulence against the widely usedrhg1‐b resistance. The present study reveals another unexpected structural feature of manyRhg1 loci, and a selectable feature that is predictive ofrhg1‐a haplotypes. -
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Karrikins (KARs) are chemicals in smoke that can enhance germination of many plants. Lactuca sativa cv. Grand Rapids (lettuce), germinates in the presence of nanomolar karrikinolide (KAR1). We found that lettuce is much less responsive to KAR2 or a mixture of synthetic strigolactone analogs, rac-GR24. We investigated the molecular basis of selective and sensitive KAR1 perception in lettuce. The lettuce genome contains two copies of KARRIKIN INSENSITIVE2 (KAI2), a receptor that is required for KAR responses in Arabidopsis thaliana. LsKAI2b is more highly expressed than LsKAI2a in dry achenes and during early stages of seed imbibition. Through cross-species complementation assays in Arabidopsis we found that LsKAI2b confers robust responses to KAR1, but LsKAI2a does not. Therefore, LsKAI2b likely mediates KAR1 responses in lettuce. We compared homology models of the ligand-binding pockets of KAI2 proteins from lettuce and a fire follower, Emmenanthe penduliflora. This identified pocket residues 96, 124, 139, and 161 as candidates that influence the ligand-specificity of KAI2. Further support for the significance of these residues was found through a broader comparison of pocket residue conservation among 324 asterid KAI2 proteins. We tested the effects of substitutions at these four positions in Arabidopsis thaliana KAI2 and found that a broad array of responses to KAR1, KAR2, and rac-GR24 could be achieved.more » « less
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