Calcium regulates primary nitrate responseassociated gene transcription in a time- and dose-dependent manner.

Abstract

Nitrate (NO3-) is the primary source of nitrogen preferred by most arable crops, including wheat. The pioneering experiment on primary nitrate response (PNR) was carried out three decades ago. Since then, much research has been carried out to understand the NO3- signaling. Nitrate is sensed by the dual affinity NO3- transceptor NPF6.3, which further relays the information to a master regulator NIN-like protein 7 (NLP7) through calcium-dependent protein kinases (CPK10, CPK30, CPK32), highlighting the importance of calcium ion (Ca2+) as one of the important secondary messengers in relaying the NO3- signaling in Arabidopsis. In a previous study, we found that Ca2+ regulates nitrogen starvation response in wheat. In this study, 10days old NO3--starved wheat seedlings were exposed to various treatments. Our study on time course changes in expression of PNR sentinel genes; NPF6.1, NPF6.2, NRT2.1, NRT2.3, NR, and NIR in wheat manifest the highest level of expression at 30min after NO3- exposure. The use of Ca2+ chelator EGTA confirmed the involvement of Ca2+ in the regulation of transcription of NPFs and NRTs as well the NO3- uptake. We also observed the NO3- dose-dependent and tissue-specificregulation of nitrate reductase activity involving Ca2+ as a mediator. The participation of Ca2+ in the PNR and NO3- signaling in wheat is confirmed by pharmacological analysis, physiological evidences, and protoplast-based Ca2+ localization.