Ubiquitin ligase EL5 maintains the viability of root meristems by influencing cytokinin-mediated nitrogen effects in rice

Mochizuki, Susumu; Nakamura, Hidemitsu; Koiwai, Hanae; Sasaki, Keisuke; Kamiya, Yûji; Ichikawa, Hiroaki; Minami, Eiichi

doi:10.1093/jxb/eru110

Cited by 32 publications

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“…These results strongly suggest that the higher basal cytokinin levels, which were further increased after nitrite treatment, led to higher nitrogen sensitivity, and thus to RAM death in mEL5. 5 Consistent with the phytohormone profile, microarray analysis revealed that nitrite treatment increased the expression of a cytokinin biosynthesis gene (OsIPT4) and cytokinin-responsive genes including type-A cytokinin-response regulator genes and endogenous EL5. Interestingly, in mEL5 roots, the expression of these genes was elevated prior to nitrite treatment.…”

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confidence: 74%

“…Y. Jikumaru and Y. Kamiya of RIKEN, revealed that the mEL5 roots contained significantly more cytokinins [trans-zeatin and N 6 -(D 2 -isopentenyl)adenine] than NT. 5 Nitrite treatment increased the trans-zeatin content in both mEL5 and NT roots. Simultaneous treatment with nitrite and cytokinin or treatment with a higher amount of cytokinin also induced root cell death in NT.…”

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confidence: 91%

“…Thus, we further investigated the function of EL5 in response to nitrogen during root formation. 5 We analyzed nitrite-induced root cell death by focusing on the hormone contents, global transcriptome profile, and accumulation of superoxide and nitric oxide (NO).The expression of EL5 in roots was upregulated by cytokinin and the regenerating mEL5 plants were morphologically similar to non-transgenic (NT) controls treated with excess cytokinin; this implied that EL5 might be involved in a cytokinin pathway in roots. 4,8 Indeed, the quantification of phytohormones in whole roots, which was performed in collaboration with Drs.…”

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confidence: 99%

“…4 Recently, we reported that the nitrogen source in the medium, and particularly nitrate forms, is a cause of RAM cell death in rice plants overexpressing EL5V162A (hereafter named mEL5). 5 The chemical form and dose of nitrogen influences root formation. 6,7 In general, root elongation and lateral root development are stimulated at low-nitrogen concentrations, while highnitrogen concentrations affect root growth negatively.…”

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Rice ubiquitin ligase EL5 prevents root meristematic cell death under high nitrogen conditions and interacts with a cytosolic GAPDH

Mochizuki

Koiwai

Kondo

et al. 2015

Plant Signaling & Behavior

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Root formation in rice transformants overexpressing mutated EL5 (mEL5) was severely inhibited because of meristematic cell death. Cell death was caused by nitrogen sources, particularly nitrate forms, in the culture medium. Nitrite treatment increased the cytokinin contents in roots, but mEL5 contained more cytokinins than nontransformants. Transcriptome profiling showed overlaps between nitrite-responsive genes in non-transformants and genes with altered expression in untreated mEL5. These results indicate that impairment of EL5 function activates nitrogen signaling despite the absence of a nitrogen source. Physical interaction between the EL5 C-terminal region and a cytosolic glyceraldehyde-3-phosphate dehydrogenase, OsGapC2, was demonstrated in vitro and in vivo. Elucidation of the role of glyceraldehyde-3-phosphate dehydrogenase in oxidative cell death in plants is expected in future.Rice EL5 is a RING-H2 protein of the plant-specific ATL family 1 and has ubiquitin ligase (E3) activity. 2 Mutated RING-H2 domains show varying decreases in E3 activity depending on the degree of interaction with the ubiquitin-conjugating enzyme, OsUBC5b; proteins with W165A and V162A substitutions completely and partially lost E3 activity, respectively, in vitro. 3Overexpression of EL5W165A resulted in no root regeneration while EL5V162A overexpressors partially regenerated roots. 4 These results, coupled with microscopic observations, led us to conclude that EL5 plays a major role in maintaining cell viability in the root apical meristem (RAM) after the initiation of crown and lateral root primordia formation. 4 Recently, we reported that the nitrogen source in the medium, and particularly nitrate forms, is a cause of RAM cell death in rice plants overexpressing EL5V162A (hereafter named mEL5). 5The chemical form and dose of nitrogen influences root formation. 6,7 In general, root elongation and lateral root development are stimulated at low-nitrogen concentrations, while highnitrogen concentrations affect root growth negatively. Although root formation under various changes in nitrogen status should rely on the activity of the RAM, the ways in which the activity or viability of the RAM is maintained are largely unknown. Thus, we further investigated the function of EL5 in response to nitrogen during root formation. 5 We analyzed nitrite-induced root cell death by focusing on the hormone contents, global transcriptome profile, and accumulation of superoxide and nitric oxide (NO).The expression of EL5 in roots was upregulated by cytokinin and the regenerating mEL5 plants were morphologically similar to non-transgenic (NT) controls treated with excess cytokinin; this implied that EL5 might be involved in a cytokinin pathway in roots. 4,8 Indeed, the quantification of phytohormones in whole roots, which was performed in collaboration with Drs. Y. Jikumaru and Y. Kamiya of RIKEN, revealed that the mEL5 roots contained significantly more cytokinins [trans-zeatin and N 6 -(D 2 -isopentenyl)adenine] than NT. 5 Nitrite treatment in...

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confidence: 74%

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confidence: 91%

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confidence: 99%

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confidence: 99%

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confidence: 99%

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