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Abstract

Abstract Soluble N-ethyl-maleimide sensitive factor attachment adaptor protein receptor (SNARE) domain-containing proteins were mainly involved in vesicle-associated membrane fusion. Genetic screening has revealed the function of SNARE in different aspects of plant biology. Among them, Synthaxin-22 (SYP22) a Qa-SNARE has been reported to have a pleiotropic function in plant development including regulation of leaf waving, shoot gravitropism and flowering time. In this study, we identified a new role of SYP22 in regulation of brassinosteroid (BR) signaling, especially in the dark. SYP22 interacts with BR receptor, brassinosteroid insensitive 1 (BRI1), and overexpression of SYP22 enhanced a weak BRI1 mutant bri1-5 phenotype. syp22 mutant exhibits short hypocotyl and it is sensitive to exogenously treated BR while slightly insensitive to BR-biosynthesis inhibitor propiconazole (PCZ) in the dark. Expression levels of BR signaling maker genes ACS5, SAUR15 and IAA19 were slightly higher, while BR6OX2, a BR biosynthesis marker gene, was lower in syp22 compared to the wild-type. In addition, syp22 was sensitive to 2,4-D, a synthetic auxin, in the dark. In conclusion, SYP22 is involved in BR- and auxin-mediated hypocotyl growth inhibition in the dark, which might be via interaction with BR and auxin key regulators to alter their internalization in Arabidopsis.
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Authors and Affiliations

Ting Shan Yao
Xiao Feng Zhu
Jin Hee Jung
Yuan Hu Xuan
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Abstract

Abstract NH4+ is an important N-source which regulates plant growth and development. However, the underlying mechanism of NH4+ uptake and its-mediated signaling is poorly understood. Here, we performed phosphoproteomic studies using the titanium dioxide (TiO2)-mediated phosphopeptides collection method together with LC-MS analysis. The results indicated that phosphorylation levels of 23 and 43 peptides/proteins involved in diverse aspects, including metabolism, transport and signaling pathway, were decreased and increased respectively after NH4+ treatment in rice roots. Among 23 proteins detected, IDD10, a key transcription factor in ammonium signaling, was identified to reduce phosphorylation level of S313 residue. Further biochemical analysis using IDD10-GFP transgenic plants and immunoprecipitation assay confirmed that NH4+ supply reduces IDD10 phosphorylation level. Phosphorylation of ammonium transporter 1;1 (AMT1;1) was increased upon NH4+ treatment. Interestingly, phosphorylation of T446, a rice specific residue against Arabidopsis was identified. It was also established that phosphorylation of T452 is conserved with T460 of Arabidopsis AMT1;1. Yeast complementation assay with transformation of phosphomimic forms of AMT1;1 (T446/D and T452/D) into 31019b strain revealed that phosphorylation at T446 and T452 residues abolished AMT1;1 activity, while their plasma membrane localization was not changed. Our analyses show that many proteins were phosphorylated or dephosphorylated by NH4+ that may provide important evidence for studying ammonium uptake and its mediated signaling by which rice growth and development are regulated.
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Authors and Affiliations

Xiao Feng Zhu
Wan Hui Cai
Jin Hee Jung
Yuan Hu Xuan

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