A NIGT1-centred transcriptional cascade regulates nitrate signalling and incorporates phosphorus starvation signals in Arabidopsis

Abstract

Nitrate is a nutrient signal that triggers complex regulation of transcriptional networks to modulate nutrient-dependent growth and development in plants. This includes time- and nitrate concentration-dependent regulation of nitrate-related gene expression. However, the underlying mechanisms remain poorly understood. Here we identify NIGT1 transcriptional repressors as negative regulators of the Arabidopsis NRT2.1 nitrate transporter gene, and show antagonistic regulation by NLP primary transcription factors for nitrate signalling and the NLP-NIGT1 transcriptional cascade-mediated repression. This antagonistic regulation provides a resolution to the complexity of nitrate-induced transcriptional regulations. Genome-wide analysis reveals that this mechanism is applicable to NRT2.1 and other genes involved in nitrate assimilation, hormone biosynthesis and transcription. Furthermore, the PHR1 master regulator of the phosphorus-starvation response also directly promotes expression of NIGT1 family genes, leading to reductions in nitrate uptake. NIGT1 repressors thus act in two transcriptional cascades, forming a direct link between phosphorus and nitrogen nutritional regulation.

Nitrogen–phosphorus interplay: old story with molecular tale

“…This cascade underlies the working mechanism behind nitrate-promoted N-P-coordinated utilization. Additionally, the expression of NIGT1 can also respond to phosphate availability, possibly under the control of both PHR and NLP (Maeda et al, 2018). Note that, besides nitrate, ammonium is also the major N source and the signal molecule for plants (Liu & von Wir en, 2017).…”

“…The N-regulated P response has been well described by recent studies, while the Pregulated N response remains largely obscure. Phosphate availability can dramatically regulate the expression of nitrate responsive genes in both Arabidopsis and rice (Maeda et al, 2018;Hu et al, 2019;Medici et al, 2019). AtNRT1.5, a nitrate transporter responsible for root-toshoot nitrate transport, is also reported to be involved in regulating the phosphate starvation response in Arabidopsis (Cui et al, 2019).…”

“…Tansley insight New Phytologist would allow plants to optimize N utilization under different N conditions (Maeda et al, 2018). Moreover, they can also target the repressor genes of the phosphate starvation response, including AtSPX1/2/4 and AtPHO2, thus activating phosphate utilization .…”

The long noncoding RNA T5120 regulates nitrate response and assimilation in Arabidopsis

“…Konishi & Yanagisawa, 2013;Marchive et al, 2013;Guan et al, 2017). Moreover, NLP7 also regulates the nitrate signalling by directly binding to the promoter and controlling the expression of NIGT1, which encodes the GARP-type transcriptional repressor 1 proteins and affects the expression of some target genes involved in nitrate regulation (Maeda et al, 2018). Interestingly, our study reveals that NLP7 works upstream of T5120 to regulate the nitrate signalling.…”

“…NLP7 directly binds to some nitrate‐related genes, including NIR , NRT2.1 , and NRT2.2 , controlling their transcription levels and then modulating nitrate transport and assimilation (Castaings et al ., ; Konishi & Yanagisawa, ; Marchive et al ., ; Guan et al ., ). Moreover, NLP7 also regulates the nitrate signalling by directly binding to the promoter and controlling the expression of NIGT1 , which encodes the GARP‐type transcriptional repressor 1 proteins and affects the expression of some target genes involved in nitrate regulation (Maeda et al ., ). Interestingly, our study reveals that NLP7 works upstream of T5120 to regulate the nitrate signalling.…”