5 research outputs found
Recommended from our members
Clearing the smoke: Structural and functional insights into the Karrikin and Strigolactone signaling pathways
Plant signaling pathways control all aspects of plant physiology and development, providing plants with the flexibility to respond to both internal and external cues. In recent years there has been a growing body of research dedicated to plant phytohormones and understanding the interplay between hormone signaling pathways. In my research work, I explored the karrikin (KAR) signaling pathway, a small molecule-induced network initially found to be responsive to smoke, but now recognized for its diverse effects on plant phenotypes in the absence of fire. In this thesis and elsewhere, there is substantial evidence that KAR signaling is a novel hormone signaling network. In this PhD research I have pushed the boundaries of knowledge in this KAR signaling field.In the first chapter I introduce the critical functions of the KAR signaling pathway and its intricate relation with the phytohormone strigolactone (SL). I delve into the intriguing story of how KAR signaling came to be known as ‘KL’, an undiscovered endogenous signaling pathway with broad implications for plant growth and development.
The second chapter presents the results of a study investigating the effect of duplicating the KAR receptor, KAI2 across evolutionary time. This chapter illustrates how receptors can fine-tune their sensitivity to different ligands by modifying just a few amino acids in the ligand-binding pocket. Additionally, I reveal a novel ligand-bound intermediate structure of KAI2, shedding light on the complex mode of ligand interaction and hydrolysis.
In the third chapter I explore mutational studies of the KAI2 receptor, examining again its ligand binding pocket. I show how one mutation can enhance sensitivity while another diminishes it. I also examine perturbation to the protein-protein interaction interface of KAI2 with its binding partner, MAX2, revealing residues and hydrophobic interactions that contribute to this interaction.
In the fourth chapter I investigate a novel KL discovered in petunia, which exerts broad effects on floral development. I untangle the intricate relations between this novel KL, its ability to induce a KL molecular response, and its reliance on the KAR/KL signaling pathway to do so.
In the fifth chapter I reveal the dynamics within the KL signaling protein MAX2, demonstrating how conformational changes affect its ability to mediate ubiquitination and degradation of target substrates, as well as its impact on the activity of the receptor protein binding partner.
In the sixth and final chapter I introduce a new area of research that I have pioneered, exploring the interactome of the KL signaling pathway in plants. Here I offer insights into potential novel proteins involved in the KL signaling pathway, as well as those that regulate or engage in cross-talk between KL and other hormone signaling pathways
Recommended from our members
Strigolactones: diversity, perception, and hydrolysis
Strigolactones (SLs) are a unique and novel class of phytohormones that regulate numerous processes of growth and development in plants. Besides their endogenous functions as hormones, SLs are exuded by plant roots to stimulate critical interactions with symbiotic fungi but can also be exploited by parasitic plants to trigger their seed germination. In the past decade, since their discovery as phytohormones, rapid progress has been made in understanding the SL biosynthesis and signaling pathway. Of particular interest are the diversification of natural SLs and their exact mode of perception, selectivity, and hydrolysis by their dedicated receptors in plants. Here we provide an overview of the emerging field of SL perception with a focus on the diversity of canonical, non-canonical, and synthetic SL probes. Moreover, this review offers useful structural insights into SL perception, the precise molecular adaptations that define receptor-ligand specificities, and the mechanisms of SL hydrolysis and its attenuation by downstream signaling components
Recommended from our members
Structural insights into photoactivation of plant Cryptochrome-2.
Cryptochromes (CRYs) are evolutionarily conserved photoreceptors that mediate various light-induced responses in bacteria, plants, and animals. Plant cryptochromes govern a variety of critical growth and developmental processes including seed germination, flowering time and entrainment of the circadian clock. CRY's photocycle involves reduction of their flavin adenine dinucleotide (FAD)-bound chromophore, which is completely oxidized in the dark and semi to fully reduced in the light signaling-active state. Despite the progress in characterizing cryptochromes, important aspects of their photochemistry, regulation, and light-induced structural changes remain to be addressed. In this study, we determine the crystal structure of the photosensory domain of Arabidopsis CRY2 in a tetrameric active state. Systematic structure-based analyses of photo-activated and inactive plant CRYs elucidate distinct structural elements and critical residues that dynamically partake in photo-induced oligomerization. Our study offers an updated model of CRYs photoactivation mechanism as well as the mode of its regulation by interacting proteins
Structural and functional analyses explain Pea KAI2 receptor diversity and reveal stereoselective catalysis during signal perception
International audienceKAI2 proteins are plant α/β hydrolase receptors which perceive smoke-derived butenolide signals and endogenous, yet unidentified KAI2-ligands (KLs). The number of functional KAI2 receptors varies among species and KAI2 gene duplication and sub-functionalization likely plays an adaptative role by altering specificity towards different KLs. Legumes represent one of the largest families of flowering plants and contain many agronomic crops. Prior to their diversification, KAI2 underwent duplication resulting in KAI2A and KAI2B. Here we demonstrate that Pisum sativum KAI2A and KAI2B are active receptors and enzymes with divergent ligand stereoselectivity. KAI2B has a higher affinity for and hydrolyses a broader range of substrates including strigolactone-like stereoisomers. We determine the crystal structures of PsKAI2B in apo and butenolide-bound states. The biochemical, structural, and mass spectra analyses of KAI2s reveal a transient intermediate on the catalytic serine and a stable adduct on the catalytic histidine, confirming its role as a bona fide enzyme. Our work uncovers the stereoselectivity of ligand perception and catalysis by diverged KAI2 receptors and proposes adaptive sensitivity to KAR/KL and strigolactones by KAI2B