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Kosami, K.-i.

Publications and source records attributed to Kosami, K.-i..

3 recordsLinked to original sources
bioRxiv2021

Three conserved hydrophobic residues in the CC domain of Pit contribute to its plasma membrane localization and immune induction

Nucleotide-binding leucine-rich repeat (NLR) proteins work as crucial intracellular immune receptors. N-terminal domains of NLRs fall into two groups, namely coiled-coil (CC) and Toll-interleukin 1 receptor (TIR) domains, which play critical roles in signal transduction and disease resistance. However, the activation mechanisms of NLRs, and how their N-termini are involved in immune induction, remain largely unknown. Here, we revealed that the rice NLR Pit self-associates through its CC domain. The CC domain of Pit possesses three conserved hydrophobic residues that are known to be involved in homodimer formation in two NLRs, barley MLA10 and Arabidopsis RPM1. Interestingly, the function of these residues in Pit is different from that in MLA10 and RPM1. Although the three hydrophobic residues are important for Pit-induced disease resistance against rice blast fungus, they do not participate in self-association or in binding to downstream signaling molecules. Based on homology modeling of Pit using the structure of the Arabidopsis NLR ZAR1, we tried to clarify the role of the three conserved hydrophobic residues and found that they are involved in the plasma membrane localization. Our findings provide novel insights for understanding the mechanisms of NLR activation as well as the relationship between subcellular localization and immune induction.

plant biology↗
bioRxiv2020

The Small GTPase OsRac1 forms two distinct immune receptor complexes containing the PRR OsCERK1 and the NLR Pit

Plants employ two different types of immune receptors, cell surface pattern recognition receptors (PRRs) and intracellular nucleotide-binding and Leucine-rich repeat-containing proteins (NLRs), to cope with pathogen invasion. Both immune receptors often share similar downstream components and responses but it remains unknown whether a PRR and an NLR assemble into the same protein complex or two distinct receptor complexes. We have previously found that the small GTPase OsRac1 plays key roles in the signaling of OsCERK1, a PRR for fungal chitin, and of Pit, an NLR for rice blast fungus, and associates directly and indirectly with both of these immune receptors. In this study, using biochemical and bioimaging approaches, we reveal that OsRac1 formed two distinct receptor complexes with OsCERK1 and with Pit. Supporting this result, OsCERK1 and Pit utilized different transport systems for anchorage to the plasma membrane. Activation of OsCERK1 and Pit led to OsRac1 activation and, concomitantly, OsRac1 shifted from a small to a large protein complex fraction. We also found that the chaperone Hsp90 contributed to the proper transport of Pit to the plasma membrane and the immune induction of Pit. These findings illuminate how the PRR OsCERK1 and the NLR Pit orchestrate rice immunity through the small GTPase OsRac1.Competing Interest StatementThe authors have declared no competing interest.View Full Text

plant biology↗
bioRxiv2018

In vivo monitoring of plant small GTPase activation using a Förster resonance energy transfer biosensor

Small GTPases act as molecular switches that regulate various plant responses such as disease resistance, pollen tube growth, root hair development, cell wall patterning and hormone responses. Thus, to monitor their activation status within plant cells is believed to be the key step in understanding their roles. We have established a plant version of a Forster resonance energy transfer (FRET) probe called Ras and interacting protein chimeric unit (Raichu) that can successfully monitor activation of the rice small GTPase OsRac1 during various defence responses in rice cells. Here, we describe the protocol for visualizing spatiotemporal activity of plant Rac/ROP GTPase in living plant cells, transfection of rice protoplasts with Raichu-OsRac1 and acquisition of FRET images. Our protocol should be widely adaptable for monitoring activation for other plant small GTPases and for other FRET sensors in various plant cells.

plant biology↗