Biology subjects

Iwakawa, H.

Publications and source records attributed to Iwakawa, H..

5 recordsLinked to original sources

bioRxiv2025

Arabidopsis epigenetic factor AS2 attenuates nucleolar stress by camptothecin and establishes leaf polarity by repressing a CDK inhibitor

The Arabidopsis thaliana leaf, exhibiting a symmetrically extended flat morphology, consists of two distinct cellular domains: adaxial and abaxial layers. The ASYMMETRIC LEAVES2 (AS2) gene is essential for specifying the adaxial domain, and its protein forms nucleolar structures, termed AS2 bodies, at ribosomal-DNA loci. Numerous nucleolus-related genes have been reported to be cooperatively involved in leaf adaxialization together with AS2. However, the molecular relationships between AS2 and these genes remain unclear. To identify chemical modulators of AS2 function, we screened a chemical library containing natural products and identified eight molecules, including camptothecin, that induced filamentous leaves in the as2 mutant. Camptothecin is an inhibitor of topoisomerase I, which is required for transcription of ribosomal-RNA genes, and induces nucleolar stress. Treatment with 10-hydroxy-camptothecin increased KIP-RELATED-PROTEIN5/INHIBITOR-OF-CYCLIN-DEPENDENT-KINASE3 (KRP5/ICK3) transcript levels, encoding a CDK inhibitor, and caused notable changes in the number and morphology of AS2 bodies. Given its role in leaf morphogenesis, our findings suggest that AS2 is a key factor in establishing leaf adaxial-abaxial polarity by regulating cell proliferation and protecting against nucleolar stress through coordinated interactions with nucleolar proteins.

developmental biology↗

bioRxiv2022

Genetic and phosphoproteomic basis of LysM-mediated immune signaling in Marchantia polymorpha highlights conserved elements and new aspect of pattern-triggered immunity in land plants

Pattern-recognition receptor (PRR)-triggered immunity (PTI) wards off a wide range of pathogenic microbes, playing a pivotal role in plant immunity. The model liverwort Marchantia polymorpha is emerging as a popular model for investigating the evolution of plant-microbe interactions. M. polymorpha triggers defense-related gene expression upon sensing components of bacterial and fungal extracts, suggesting the existence of PTI in this plant model. However, the molecular components of the putative PTI in M. polymorpha have not yet been described. We show that, in M. polymorpha, which has four LysM receptor homologs, lysin motif (LysM) receptor-like kinase (LYK) MpLYK1 and LYK-related (LYR) MpLYR are required for sensing chitin and peptidoglycan fragments, triggering a series of characteristic immune responses. Comprehensive phosphoproteomic analysis of M. polymorpha in response to chitin treatment identified regulatory proteins that potentially shape LysM-mediated PTI. The identified proteins included homologs of well-described PTI components in angiosperms as well as proteins whose roles in PTI are not yet determined, including the blue-light receptor phototropin MpPHOT. We revealed that MpPHOT is required for a negative feedback of defense-related gene expression during PTI. Taken together, this study outlines the basic framework of LysM-mediated PTI in M. polymorpha and demonstrates the utility of M. polymorpha as a plant model for discovering novel or fundamental molecular mechanisms underlying PRR-triggered immune signaling in plants.

plant biology↗

bioRxiv2022

The canonical E2Fs together with RETINOBLASTOMA-RELATED are required to establish quiescence during plant development

Maintaining stable and transient quiescence in differentiated and stem cells, respectively, requires repression of the cell cycle. The plant RETINOBLASTOMA-RELATED (RBR) has been implicated in stem cell maintenance, presumably by forming repressor complexes with E2F transcription factors. Surprisingly we find that mutations in all three canonical E2Fs do not compromise the cell cycle, but similarly to RBR silencing, result in overproliferation. Contrary to the growth arrest upon RBR silencing, when exit from proliferation to differentiation is inhibited, the e2fabc mutant develops enlarged organs with supernumerary stem and differentiated cells as the quiescence is compromised. While E2F, RBR and the M-phase regulatory MYB3Rs are part of the DREAM repressor complexes, and recruited to overlapping groups of targets, they regulate distinct sets of genes. Only the loss of E2Fs but not the MYB3Rs interferes with quiescence, which might be due to the ability of E2Fs to control both G1-S and some key G2-M targets. We conclude that collectively the three canonical E2Fs in complex with RBR have central roles in establishing cellular quiescence during organ development, leading to enhanced plant growth.

plant biology↗

bioRxiv2022

Contrasting and conserved roles of NPR proteins in diverged land plant lineages

The NPR proteins function as salicylic acid (SA) receptors in Arabidopsis thaliana. AtNPR1 plays a central role in SA-induced transcriptional reprogramming whereby positively regulates SA-mediated defense. NPRs are found in the genomes of nearly all land plants. However, we know little about the molecular functions and physiological roles of NPRs in most plant species. Our phylogenetic and alignment analyses show that Brassicaceae NPR1-like proteins have characteristically gained or lost functional residues or motifs identified in AtNPRs, pointing to the possibility of a unique evolutionary trajectory for the Brassicaceae NPR1-like proteins that has resulted in peculiar functions. In line with this observation, we find that the only NPR in Marchantia polymorpha, MpNPR, is not the master regulator of SA-induced transcriptional reprogramming and negatively regulates bacterial resistance in this species. Interspecies complementation analysis indicated that the molecular properties of AtNPR1 and MpNPR are partially conserved, implying the diversification of NPR-associated pathways contributed to distinct roles of NPR in different species. The Mpnpr transcriptome suggested potential roles of MpNPR in heat and far-red light responses. We identify both Mpnpr and Atnpr1-1 display enhanced thermomorphogenesis. NPRs and NPR-associated pathways clearly have evolved distinctively in diverged land plant lineages to cope with different terrestrial environments.

plant biology↗

bioRxiv2021

Agrobacterium-Mediated Transient Transformation of Marchantia Liverworts

Agrobacterium-mediated transient gene expression is a rapid and useful approach for characterizing functions of gene products in planta. However, the practicability of the method in the model liverwort Marchantia polymorpha has not yet been thoroughly described. Here we report a simple and robust method for Agrobacterium-mediated transient transformation of Marchantia thalli and its applicability. When thalli of M. polymorpha were co-cultured with Agrobacterium tumefaciens carrying GUS genes, GUS staining was observed primarily in assimilatory filaments and rhizoids. GUS activity was detected 2 days after infection and saturated 3 days after infection. We were able to transiently co-express fluorescently tagged proteins with proper localizations. Furthermore, we demonstrate that our method can be used as a novel pathosystem to study liverwort-bacteria interactions. We also provide evidence that air chambers support bacterial colonization.

plant biology↗