Biology subjects

Majhi, B. B.

Publications and source records attributed to Majhi, B. B..

3 recordsLinked to original sources

bioRxiv2022

Characterization of norbelladine synthase and noroxomaritidine/norcraugsodine reductase reveals a novel catalytic route for the biosynthesis of Amaryllidaceae alkaloids including the Alzheimer's drug galanthamine

Amaryllidaceae alkaloids (AAs) are a large group of pharmacological plant-specialized metabolites. Norbelladine is the entry compound in AAs biosynthesis. Two enzymes are capable of catalyzing this reaction in-vitro, both with low-yield; 1) norbelladine synthase (NBS) condenses tyramine and 3,4-dihydroxybenzaldehyde, while 2) noroxomaritidine/norcraugsodine reductase (NR), catalyzes a reduction reaction. To clarify the mechanisms involved in this controversial step, both NBS and NR were characterized from Narcissus papyraceus and Leucojum aestivum. Assays with each enzyme suggested that NBS and NR function together for norbelladine formation. Using molecular-homology modeling and docking studies, we predicted models for the binding of substrates to NBS and NR. Moreover, NBS and NR physically interact, localize to the cell cytoplasm and nucleus and are expressed at high levels in bulbs. Our study establishes that both NBS and NR participate in the biosynthesis of norbelladine, catalyzing the first key steps involved in the biosynthesis of the Alzheimers drug galanthamine.

biochemistry↗

bioRxiv2022

Tomato brassinosteroid-signaling kinase Bsk830 is a component of flagellin signaling that regulates pre-invasion immunity

Detection of bacterial flagellin by the tomato receptors Flagellin sensing 2 (Fls2) and Fls3 triggers activation of pattern-triggered immunity (PTI). Tomato signaling components associated or downstream of flagellin receptors are largely unknown. We investigated the involvement of tomato brassinosteroid-signaling kinase 830 (Bsk830) in PTI triggered by flagellin perception. Bsk830 localized to the plasma membrane and interacted with Fls2 and Fls3. Consistent with a role in flagellin- induced signaling, CRISPR/Cas9-generated tomato bsk830 mutants were impaired in ROS accumulation induced by the flagellin-derived flg22 and flgII-28 peptides. In addition, bsk830 mutants developed larger populations of Pseudomonas syringae pv. tomato (Pst) strain DC3000 than wild-type plants, whereas no differences were observed in plants infected with the flagellin deficient Pst DC3000{Delta}fliC. bsk830 mutants failed to close stomata when infected with Pst DC3000 and Pseudomonas fluorescens, and were more susceptible to Pst DC3000 than wild-type plants when inoculated by dipping, but not by vacuum-infiltration, indicating involvement of Bsk830 in pre-invasion immunity. Analysis of gene expression profiles in bsk830 mutants detected a reduced number of differentially expressed genes and altered expression of jasmonic acid (JA)-related genes. In support of deregulation of JA response in bsk830 mutants, these plants were similarly susceptible to Pst DC3000 and to the Pst DC3118 strain, which is deficient in coronatine production, and more resistant to the necrotrophic fungus Botrytis cinerea following PTI activation. These results indicate that tomato Bsk830 is required for a subset of flagellin-triggered PTI responses and support a model in which Bsk830 negatively regulates JA signaling during PTI activation.

plant biology↗

bioRxiv2019

Mai1 protein acts between host recognition of pathogen effectors and MAPK signaling

The molecular mechanisms acting between host recognition of pathogen effectors by NOD-like receptor (NLR) proteins and mitogen-activated protein kinase (MAPK) signaling cascades are unknown. MAPKKK (M3K) activates MAPK signaling leading to programmed cell death (PCD) associated with NLR-triggered immunity. We identified a tomato M3K-interacting protein, SlMai1, that has 80% amino acid identity with Arabidopsis brassinosteroid kinase 1 (AtBsk1). SlMai1 has a protein kinase domain and a C-terminal tetratricopeptide repeat domain which interacts with the kinase domain of M3K. Virus-induced gene silencing of Mai1 homologs in Nicotiana benthamiana increased susceptibility to Pseudomonas syringae and compromised PCD induced by four NLR proteins. PCD was restored by expression of a synthetic SlMai1 gene that resists silencing. Expression of AtBsk1 did not restore PCD in Mai1-silenced plants, suggesting SlMai1 is functionally divergent from AtBsk1. PCD caused by overexpression of M3K or MKK2 was unaffected by Mai1 silencing indicating Mai1 acts upstream of these proteins. Co-expression of Mai1 with M3K in leaves enhanced MAPK phosphorylation and accelerated PCD. These findings reveal Mai1 as a molecular link acting between host recognition of pathogens and MAPK signaling. Author SummaryPlants use intracellular immune receptors to detect and respond to specific effector proteins which pathogens translocate into the host cell as part of their infection process. Localized programmed cell death (PCD) involving a mitogen-activated protein kinase (MAPK) cascade is an important host response associated with effector-triggered immunity, although the molecular connections between immune receptors and MAPK signaling is unknown. The Mai1 protein was found to act downstream of multiple immune receptors in Nicotiana benthamiana and to physically interact with MAPKKK. The Mai1-MAPKKK interaction enhances MAPK phosphorylation, triggers PCD and promotes disease resistance.

plant biology↗