Biology subjects

de Saint Germain, A.

Publications and source records attributed to de Saint Germain, A..

5 recordsLinked to original sources

bioRxiv2024

DWARF14 and KARRIKIN INSENSITIVE2 mediate signaling of the apocarotenoid zaxinone in Arabidopsis

The natural growth regulator zaxinone increases the levels of the phytohormones strigolactone (SL) and abscisic acid in Arabidopsis (Arabidopsis thaliana) via unknown mechanisms. We demonstrate that parts of the effects of zaxinone in Arabidopsis depend on the SL receptor DWARF14 (AtD14), the karrikin receptor KARRIKIN INSENSITIVE2 (AtKAI2), and the F-Box protein MORE AXILLARY BRANCHING2 (AtMAX2) that mediates the signaling of SLs and karrikins. Binding assays and co-crystallization revealed zaxinone as an additional ligand of AtD14 and an SL antagonist that interrupts the interaction of AtD14 with AtMAX2. Zaxinone also bound to AtKAI2. These findings unveil a perception mechanism for zaxinone in Arabidopsis and demonstrate the capability of AtD14 and AtKAI2 to bind signaling molecules, other than strigolactones or karrikins, and mediate their transduction.

plant biology↗

bioRxiv2023

Physcomitrium patens SMXL homologs are PpMAX2-dependent negative regulators of growth

SMXL proteins are a plant-specific clade of type I HSP100/Clp-ATPases. SMXL genes are found in virtually all land plant genomes. However, they have mainly been studied in angiosperms. In Arabidopsis thaliana, three SMXL functional subclades have been identified: SMAX1/SMXL2, SMXL345 and SMXL678. Out of these, two subclades ensure transduction of endogenous hormone signals: SMAX1/SMXL2 are involved in KAI2-ligand (KL) signaling, while SMXL678 are involved in strigolactone (SL) signaling. Many questions remain regarding the mode of action of these proteins, as well as their ancestral role. We addressed these questions by investigating the function of the four SMXL genes of the moss Physcomitrium patens. We demonstrate that PpSMXL proteins are involved in the conserved ancestral MAX2-dependent KL signaling pathway and act as negative regulators of growth. However, PpSMXL proteins expressed in A. thaliana unexpectedly cannot replace SMAX1/SMXL2 function in KL signaling, whereas they can functionally replace SMXL4/5 and restore root growth. Therefore, the molecular function of SMXL could be conserved, but not their interaction network. Moreover, one PpSMXL clade positively regulates transduction of the SL signal in P. patens. So far, this function has only been reported herein in moss, where it represents a novel crosstalk between SL and KL signaling pathways.

plant biology↗

bioRxiv2021

Structural Basis of KAI2 Divergence in Legume

KAI2 are plant /{beta} hydrolase receptors, which perceive smoke-derived butenolide signals (karrikins) and putative endogenous, yet unidentified phytohormones (KAI2-ligands, KLs). The number of functional KAI2 receptors varies among plant species. It has been suggested that KAI2 gene duplication and sub-functionalization plays an adaptative role for diverse environments or ligand diversification by altering the receptor responsiveness to specific KLs. Legumes represent one of the largest families of flowering plants and contain many essential agronomic crops. Prior to legume diversification, KAI2 underwent duplication, resulting in KAI2A and KAI2B. Integrating plant genetics, ligand perception and enzymatic assays, and protein crystallography, we demonstrate that Pisum sativum KAI2A and KAI2B act as receptors and enzymes with divergent ligand stereoselectivity. KAI2B has a stronger affinity than KAI2A towards the KAI2-ligand (-)-GR24 and remarkably hydrolyses a broader range of substrates including the strigolactone-like isomer (+)-GR24. We determine the crystal structures of PsKAI2B in apo and butenolide-bound states. The biochemical and structural analyses as well as recorded mass spectra of KAI2s reveal a transient intermediate on the catalytic serine and a stable adduct on the catalytic histidine, further illuminating the role of KAI2 not only as receptors but also as bona fide enzymes. Our work uncovers the stereoselectivity of ligand perception and catalysis by evolutionarily diverged KAI2 receptors in KAR/KL signaling pathways and proposes adaptive sensitivity to KAR/KL and strigolactone phytohormones by KAI2B.

biochemistry↗

bioRxiv2020

A Phelipanche ramosa KAI2 Protein Perceives enzymatically Strigolactones and Isothiocyanates

Phelipanche ramosa is an obligate root-parasitic weed threatening major crops in central Europe. For its germination, it has to perceive various structurally diverging host-exuded signals, including isothiocyanates (ITCs) and strigolactones (SLs). However, the receptors involved are still uncharacterized. Here, we identified five putative SL receptors in P. ramosa, of which PrKAI2d3 is involved in seed germination stimulation. We established the high plasticity of PrKAI2d3, allowing interaction with different chemicals, including ITCs. The SL perception mechanism of PrKAI2d3 is similar to that of endogenous SLs in non-parasitic plants. We provide evidence that the PrKAI2d3 enzymatic activity confers hypersensitivity to SLs. Additionally, we demonstrated that methylbutenolide-OH binds PrKAI2d3 and stimulates P. ramosa germination with a bioactivity comparable to that of ITCs. This study highlights that P. ramosa has extended its signal perception system during evolution, a fact to be considered in the development of specific and efficient biocontrol methods.

plant biology↗

bioRxiv2020

Hormonal regulation of the BRC1-dependent strigolactone transcriptome involved in shoot branching responses

The plant hormone strigolactone (SL) inhibits shoot branching by suppressing the growth of axillary buds. This is thought to occur largely via regulation of the transcription factor BRANCHED1 (BRC1). Here, we clarify the central role of BRC1 and identify additional transcriptional responses by which SL might regulate axillary bud outgrowth in garden pea (Pisum sativum). We used a transcriptomic approach to identify differentially expressed transcripts in pea axillary buds in response to a synthetic SL, rac-GR24. Changes in transcript abundance were confirmed by measuring their response to GR245DS. BRC1 was required for the regulation of over half of the fourteen GR245DS-regulated genes, confirming its role as a mediator of SL transcriptional responses in axillary buds. All, but one, of the BRC1-dependent GR245DS-regulated genes were also regulated by branch-promoting treatments cytokinin (CK) and/or decapitation in an opposing manner to SL. This suggests that SL, CK, and decapitation regulate shoot branching via a common pathway. We used correlational analyses of gene co-expression data to infer a gene regulatory network consisting of nine key co-expression modules correlated with rac-GR24 treatment. Enrichment of GO terms such as cell proliferation, carbohydrate responses, and abscisic acid and jasmonic acid hormone pathways suggest a role for these in SL-mediated inhibition of shoot branching. In summary, we have shown that BRC1 is indeed a key transcriptional regulator of the SL signalling pathway in pea buds as well as a focal point of the SL, CK and decapitation signalling pathways to coordinate shoot branching in pea buds. One Sentence SummaryIdentification of genes that are strigolactone-responsive and BRC1-dependent in pea buds reveals a high degree of overlap among strigolactone, cytokinin and decapitation response pathways.

plant biology↗