CmNDB1 and a Specific Domain of CmMYB1 Negatively Regulate CmMYB1-Dependent Transcription of Nitrate Assimilation Genes Under Nitrogen-Repleted Condition in a Unicellular Red Alga

Baifeng Zhou,Hiroki Shima,Sousuke Imamura,Kazuhiko Igarashi,Kan Tanaka

doi:10.3389/fpls.2022.821947

Abstract

Nitrogen assimilation is an essential process that controls plant growth and development. Plant cells adjust the transcription of nitrogen assimilation genes through transcription factors (TFs) to acclimatize to changing nitrogen levels in nature. However, the regulatory mechanisms of these TFs under nitrogen-repleted (+N) conditions in plant lineages remain largely unknown. Here, we identified a negative domain (ND) of CmMYB1, the nitrogen-depleted (−N)-activated TF, in a unicellular red alga Cyanidioschyzon merolae. The ND deletion changed the localization of CmMYB1 from the cytoplasm to the nucleus, enhanced the binding efficiency of CmMYB1 to promoters of nitrate assimilation genes, and increased the transcripts of nitrate assimilation genes under +N condition. A pull-down assay using an ND-overexpressing strain combined with liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis helped us to screen and identify an unknown-function protein, the CmNDB1. Yeast two-hybrid analysis demonstrated that CmNDB1 interacts with ND. Similar to ND deletion, CmNDB1 deletion also led to the nucleus localization of CmMYB1, enhanced the promoter-binding ratio of CmMYB1 to the promoter regions of nitrate assimilation genes, and increased transcript levels of nitrate assimilation genes under +N condition. Thus, these presented results indicated that ND and CmNDB1 negatively regulate CmMYB1 functions under the +N condition in C. merolae.

Highlights

Nitrogen is a component of most basic macromolecules, including proteins and nucleic acids
Functions of transcription factors (TFs) are usually modulated by their regulatory elements that bind to cofactors and metabolite molecules (Xie et al, 2006; Puga et al, 2014; Le et al, 2016; Qi et al, 2017; Zhu et al, 2019; Wang et al, 2020) or by post-translational modifications (Gill, 2003; Tootle and Rebay, 2005; Schütze et al, 2008)
We hypothesized that the underlying mechanism related to nitrogen status-dependent CmMYB1 function could be revealed by the identification of the CmMYB1 regulatory element

Summary

Introduction

Nitrogen is a component of most basic macromolecules, including proteins and nucleic acids. Mainly ammonium and nitrate through ammonium transporter (AMT) and nitrate transporter (NRT), respectively, from their growing environments These nitrogen sources are assimilated into amino. Negative-Regulation of CmMYB1 Under +N acids through nitrogen assimilation enzymes, and these amino acids would be further utilized (Crawford and Forde, 2002) Plants alter their gene expression to acclimate to the changing nitrogen level in the environment. In Arabidopsis, recent studies have uncovered that the Nodule INception (NIN)-Like Protein 6 and 7 (NLP6, NLP7), could positively regulate the transcripts of AtNRT1.1, as well as the gene-encoding nitrate reductase (NR), AtNIA1 and AtNIA2, under −N conditions through forming a complex with TCP20 in the nucleus (Marchive et al, 2013; Guan et al, 2017). The regulators affecting the −N-activated TFs function under +N conditions in the plant kingdom are largely unknown

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Conclusion