An evolutionarily conserved nitrate sensor in plants

Abstract

Nitrogen availability in plant tissues triggers transcriptomic responses that affect not only nitrate homeostasis but also metabolic, hormonal, and developmental processes ( Wang et al., 2018 Wang Y.-Y. Cheng Y.-H. Chen K.-E. Tsay Y.-F. Nitrate transport, signaling, and use efficiency. Annu. Rev. Plant Biol. 2018; 69: 85-122 Crossref PubMed Scopus (266) Google Scholar ). The ability to sense extracellular nitrate has been attributed to the characterized nitrate transceptor NRT1.1 (CHL1/NPF6.3); however, null chl1-5 mutants are not entirely impaired in the primary nitrogen response, suggesting that there might be other sensors that act independently ( Wang et al., 2018 Wang Y.-Y. Cheng Y.-H. Chen K.-E. Tsay Y.-F. Nitrate transport, signaling, and use efficiency. Annu. Rev. Plant Biol. 2018; 69: 85-122 Crossref PubMed Scopus (266) Google Scholar ). Furthermore, the calcium-sensor protein kinases (CPKs) responsible for transducing nitrate signaling downstream, even when constitutively activated, still require the presence of nitrate ( Liu et al., 2017 Liu K. Niu Y. Konishi M. Wu Y. Du H. Sun Chung H. Li L. Boudsocq M. McCormack M. Maekawa S. et al. Discovery of nitrate–CPK–NLP signalling in central nutrient–growth networks. Nature. 2017; 545: 311-316 Crossref PubMed Scopus (275) Google Scholar ), indicating an additional nitrate-sensing mechanism. This missing link was recently identified by joint efforts between Dr. Kun-Hsiang Liu’s lab at Northwest Agriculture and Forestry University, China, and Dr. Jen Sheen’s lab at Mass General Hospital/Harvard Medical School ( Liu et al., 2022 Liu K.-H. Liu M. Lin Z. Wang Z.-F. Chen B. Liu C. Guo A. Konishi M. Yanagisawa S. Wagner G. et al. NIN-like protein 7 transcription factor is a plant nitrate sensor. Science. 2022; 377: 1419-1425 Crossref PubMed Scopus (3) Google Scholar ). Using transcriptomic, genetic, imaging, biochemical, and structural analyses, Liu et al. uncovered the role of the master transcription factor in nitrate signaling, NPL7, as an intracellular nitrate sensor (Figure 1).