Biology subjects

Nambara, E.

Publications and source records attributed to Nambara, E..

4 recordsLinked to original sources

bioRxiv2025

Over-expression of Cyclic Nucleotide-Gated Ion Channel 2 (CNGC2) triggers 1 hypersensitivity to virulent pathogens and elevated Ca2+

The Arabidopsis Cyclic Nucleotide-Gated Ion Channel 2 (CNGC2), also known as Defense No Death 1 (DND1), is the most extensively studied plant CNGC and has been implicated in diverse physiological processes, including floral transition, responses to heat and humidity, and hormone signaling. Its role in immunity has received particular attention due to the autoimmunity phenotype observed in the cngc2/dnd1 knockout mutants. Interestingly, despite this hyperactivation of immunity, the mutant also exhibits impaired hypersensitive cell death--a hallmark of effector-triggered immunity (ETI)--as well as reduced reactive oxygen species (ROS) production and diminished Ca{superscript 2} influx in response to pathogen-associated molecular patterns (PAMPs) such as the bacterial flagellin peptide flg22. These contradictory phenotypes highlight the complex biological functions of CNGC2. To date, most studies have focused on loss-of-function mutants. In this study, we performed a detailed characterization of CNGC2 overexpression lines to gain deeper insight into its role in immunity. Remarkably, overexpression of CNGC2 led to heightened susceptibility to two taxonomically distinct pathogens, despite the plants displaying wild-type morphology. Overexpression of CNGC2 rescued several cngc2 mutant phenotypes, including morphological defects and delayed flowering, yet these plants were also hypersensitive to elevated external Ca{superscript 2} levels. Furthermore, they exhibited attenuated responses to flg22, suggesting that CNGC2 does not act as a simple positive or negative regulator of immunity. Our findings reveal an essential role for CNGC2 where a balanced expression level is critical for maintaining Ca{superscript 2} homeostasis between the apoplast and cytosol, thereby influencing the generation of Ca{superscript 2} signals essential for immune responses.

plant biology↗

bioRxiv2025

Evolutionary Trade-off Between Stomatal Defense and Gas Exchange in Brassicaceae

Stomatal opening is crucial for gas exchange, but it unavoidably offers invasion by pathogens. In response, plants close stomata to prevent pathogen entry, while the bacterial pathogen Pseudomonas syringae pv. tomato DC3000 (Pto) produces coronatine (COR), a jasmonate (JA) mimic, to counteract this plant response. Here, we demonstrate that by COR, Pto exploits CYP707A1 activation in Arabidopsis thaliana, encoding an enzyme that degrades abscisic acid, essential for stomatal closure. Notably, COR-induction of CYP707A1 is absent in other Brassicaceae species, such as Capsella rubella and Eutrema salsugineum, rendering them resistant to Pto invasion. In contrast, in A. thaliana, CYP707A1 enables rapid stomatal opening at dawn in a JA-dependent manner, enhancing gas exchange and chlorophyll content, unlike C. rubella and E. salsugineum. Promoter-swap experiments confirm that the regulatory region of CYP707A1 underlies these evolutionary diversifications. Together, our study presents a mechanism underlying an evolutionary trade-off between stomatal defense and gas exchange.

plant biology↗

bioRxiv2023

Knockout of endoplasmic reticulum localized molecular chaperone HSP90.7 impairs seeding development and cellular auxin homeostasis in Arabidopsis

The Arabidopsis endoplasmic reticulum localized heat shock protein HSP90.7 modulates tissue differentiation and stress responses; however, complete knockout lines have not been previously reported. In this study, we identified and analyzed a mutant allele, hsp90.7-1, which did not express any protein and showed seedling lethality. Microscopic analyses revealed its essential role in male and female fertility, trichomes and root hairs development, proper chloroplast function, and in apical meristem maintenance and differentiation. Comparative transcriptome and proteome analyses also revealed a role of the protein in a multitude of cellular processes. Particularly, the auxin responsive pathway was specifically down-regulated in the hsp90.7-1 mutant seedlings. We measured a much-reduced auxin content in both root and shoot tissues. Through comprehensive histological and molecular analyses, we demonstrated PIN1 and PIN5 expressions were dramatically reduced in the mutant, and the TAA-YUCCA primary auxin biosynthesis pathway was also down-regulated, thus revealing a critical new role of HSP90.7 in the regulation of auxin responses. This study therefore not only fulfilled a gap in understanding the essential role of HSP90 paralogs in eukaryotes, but also provided a mechanistic insight on this molecular chaperone in regulating plant growth and development via modulating cellular auxin homeostasis.

plant biology↗

bioRxiv2020

The Arabidopsis gene RGO mediates cytokinin responses and increases seed yield

A novel gene, At1g77960, from Arabidopsis thaliana was characterized. At1g77960 transcripts accumulate to very high levels in plants ectopically overexpressing the Golden2-like1 (GLK1) transcription factor and is designated as a Response to GLK1 Overexpression (RGO) gene. RGO encodes a protein with domains of tandem QH and QN repeats. Transcripts and promoter GUS reporter analyses indicated that RGO is expressed in roots, leaves, stems, floral and siliques tissues but not in seeds. Expression of the RGO:YFP fusion protein demonstrated that RGO is localized to the endoplasmic reticulum. MicroRNA mediated silencing of RGO resulted in severe reductions in vegetative and root growth, delayed flowering and reduced seed yield and viability, suggesting that RGO is essential for plant development. Conversely, ectopic overexpression of RGO resulted in enhanced vegetative growth including increased axillary bud formation and a 20% higher seed yield. Stable overexpression of RGO in Brassica napus also produced a similar increase in seed yield. Cytokinin (CK) response assays including root growth, green calli formation from excised hypocotyls and chlorophyll retention during dark-induced senescence suggest that one role of RGO is to mediate CK responses in plant development. These results suggest that RGO could be a target gene for increasing crop seed yields. One-sentence summaryRGO, a novel gene from Arabidopsis, is essential for plant development, mediates CK signaling and increases seed yield in Arabidopsis and rapeseed when overexpressed.

plant biology↗