Biology subjects

Shahul Hameed, U. F.

Publications and source records attributed to Shahul Hameed, U. F..

5 recordsLinked to original sources

bioRxiv2026

Host specificity in cereal rust fungi is mediated by a conserved glycoside hydrolase family

Non-host resistance refers to the immunity of plant species to virtually all isolates of a potential pathogen and represents an underexplored avenue for breeding and engineering disease resistance. In domesticated and wild barley, cell surface-localized lectin receptor kinases (LecRKs) contribute to determining the host status to leaf rust fungi, which pose a major threat to global cereal production. Here, we identify a conserved family of leaf rust glycoside hydrolases as ligands for these barley LecRKs and show that direct ligand-receptor binding triggers immune responses. This mechanism of pathogen perception is conserved across multiple cereal species and can be functionally transferred between them. We also uncover previously uncharacterized recognition specificities among distinct LecRK variants, expanding the repertoire of LecRK-mediated rust pathogen detection. Our findings define a molecular mechanism underlying non-host resistance in cereals and provide a basis for harnessing non-host rust resistance across diverse crop-pathogen systems.

plant biology↗

bioRxiv2025

Plant-specific adaptations of the CDC48 unfoldase

Targeted protein degradation through the CDC48 unfoldase enables the maintenance and rapid adaptation of proteomes across eukaryotes. However, the profound differences between animals, fungi, and plants are expected to have led to a significant adaptation of the CDC48-mediated degradation. While animal and fungal CDC48 systems have shown structural and functional preservation, such analysis is lacking for plants. We determined the structural and functional characteristics of Arabidopsis thaliana CDC48A in various states and bound to the target-identifying cofactors UFD1 and NPL4. Our analysis reveals several features that distinguish AtCDC48 from its animal and yeast counterparts, despite an 80% sequence identity. Key features are that AtCDC48A displays distinct domain dynamics and interacts differently with AtNPL4. Moreover, AtNPL4 and AtUFD1 do not form an obligate heterodimer, but independently bind to AtCDC48A and mediate target degradation; however, their joint action is synergistic. An evolutionary analysis supports that these Arabidopsis features are conserved across plants and represent the ancestral state of eukaryotic CDC48 systems. Jointly, our findings support that plant CDC48 retains a greater modular and combinatorial cofactor usage, highlighting a specific adaptation of targeted protein degradation in plants.

plant biology↗

bioRxiv2024

Mechanism of cooperative strigolactone perception by the MAX2 ubiquitin ligase-receptor-substrate complex

Strigolactones (SLs) are a group of plant hormones that regulate various aspects of plant growth and development. Additionally, SLs exuded into the soil promote symbiotic relationships with arbuscular mycorrhizal fungi and stimulate the germination of parasitic plants such as Striga hermonthica. The binding and hydrolysis of SLs by their receptors (D14 in Arabidopsis and HTL in Striga) promote the ubiquitination of transcriptional repressors by Skp1-cullin-F-box (SCF)-type E3 ubiquitin ligases. The mechanistic link between SL perception by D14/HTL and substrate recognition by the E3 remains unclear. We identified an E3-HTL-substrate complex that is sufficiently stable for cryogenic electron microscopy. This complex, composed of SKP1 (ASK1) and substrate (SMAX1) from Arabidopsis, and Striga F-box (MAX2) and SL receptor (HTL7), reveals that the substrate engages in a bidentate association through its N and D2 domains. This interaction, which is both conformationally and compositionally dynamic, directly and allosterically stabilises the MAX2-(SL)HTL7 complex and affects the positioning of ASK1 relative to MAX2. This dynamic positioning influences the proximity between the substrate D2 domain and the ubiquitin-conjugated E2 enzyme. This work advances our understanding of how E3 ligases in plants translate hormone perception into genetic adaptations.

biophysics↗

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↗

bioRxiv2020

Molecular Basis for the Adaptive Evolution of Environment Sensing by H-NS Proteins

The DNA-binding protein H-NS is a pleiotropic gene regulator in gram-negative bacteria. Through its capacity to sense temperature and other environmental factors, H-NS allows pathogens like Salmonella to adapt their gene expression, and hence toxicity and biological responses, to their presence inside or outside warm-blooded hosts. To investigate how this sensing mechanism may have evolved to fit different bacterial lifestyles, we compared H-NS orthologs from bacteria that infect humans, plants, and insects, and from bacteria that live on a deep-sea hypothermal vent. The combination of biophysical characterization, high-resolution proton-less NMR spectroscopy and molecular simulations revealed, at an atomistic level, how the same general mechanism was adapted to specific habitats and lifestyles. In particular, we demonstrate how environment-sensing characteristics arise from specifically positioned intra- or intermolecular electrostatic interactions. Our integrative approach clarified the mechanism for H-NS-mediated environmental sensing and suggests that it resulted from the exaptation of an ancestral protein feature.

biochemistry↗