The Calcium Ion Is a Second Messenger in the Nitrate Signaling Pathway of Arabidopsis

Abstract

Understanding how plants sense and respond to changes in nitrogen availability is the first step toward developing strategies for biotechnological applications, such as improvement of nitrogen use efficiency. However, components involved in nitrogen signaling pathways remain poorly characterized. Calcium is a second messenger in signal transduction pathways in plants, and it has been indirectly implicated in nitrate responses. Using aequorin reporter plants, we show that nitrate treatments transiently increase cytoplasmic Ca 2+ concentration. We found that nitrate also induces cytoplasmic concentration of inositol 1,4,5-trisphosphate. Increases in inositol 1,4,5-trisphosphate and cytoplasmic Ca 2+ levels in response to nitrate treatments were blocked by U73122, a pharmacological inhibitor of phospholipase C, but not by the nonfunctional phospholipase C inhibitor analog U73343. In addition, increase in cytoplasmic Ca 2+ levels in response to nitrate treatments was abolished in mutants of the nitrate transceptor NITRATE TRANSPORTER1.1/Arabidopsis (Arabidopsis thaliana) NITRATE TRANSPORTER1 PEPTIDE TRANSPORTER FAMILY6.3. Gene expression of nitrate-responsive genes was severely affected by pretreatments with Ca 2+ channel blockers or phospholipase C inhibitors. These results indicate that Ca 2+ acts as a second messenger in the nitrate signaling pathway of Arabidopsis. Our results suggest a model where NRT1.1/AtNPF6.3 and a phospholipase C activity mediate the increase of Ca 2+ in response to nitrate required for changes in expression of prototypical nitrate-responsive genes.

The calcium sensor CBL7 modulates plant responses to low nitrate in Arabidopsis

“…In addition to being an essential nutrient, nitrate also acts as a signaling molecule to regulate the expression of hundreds of nitrate-related genes [18,19]. Recent evidences showed that Ca 2þ also acts as second messenger in the nitrate signaling pathway in Arabidopsis, since an increase in cytoplasmic Ca 2þ levels in response to nitrate treatments was observed, and the expression of nitrate responsive genes was severely affected by pretreatments with Ca 2þ channel blockers [20]. Although whether nitrate deficiency could directly induce a cellular Ca 2þ signals still remained unknown, it has been proved that K þ transport in plants may somehow relate to NO 3 À transport, and nitrate deficiency could trigger a K þ transport defect [21], and furthermore, K þ transport deficiency could induce cytoplasmic Ca 2þ elevation [22].…”

Discovery of nitrate–CPK–NLP signalling in central nutrient–growth networks

“…1f). Unlike the transient and acute [Ca 2+ ]cyt increase stimulated by osmotic and cold stresses in seedlings 26,37 , nuclear Ca 2+ oscillation in symbiosis 38 , or a 10 sec [Ca 2+ ]cyt peak triggered by nitrate in roots 33 , a gradually rising subcellular Ca 2+ signature attributed to nitrate over a course of minutes was recorded by GCaMP6-based imaging with high subcellular resolution. Time-lapse recording using transgenic GCaMP6 plants uncovered a Ca 2+ signature of similar amplitude and dynamic stimulated by nitrate in mesophyll cells of intact plants (Fig.…”

“…Although nitrate-triggered Ca 2+ signals could be detected using transgenic aequorin seedlings 26,33 , the response was subtle when compared with the flg22-induced Ca 2+ signals in immune signalling (Extended Data Fig. 1b, c).…”

“…Although a role of Ca 2+ signalling in nitrate responsive gene regulation has been implicated in maize leaves and Arabidopsis roots 32,33 , many outstanding questions remained in both plants and animals, such as whether distinct Ca 2+ signatures are involved in primary nutrient signalling with cell specificity, the specific patterns of Ca 2+ dynamics, the identity of intracellular Ca 2+ sensors, how Ca 2+ sensors relay signalling specificity, and the downstream targets of Ca 2+ signalling in the nutrient-growth regulatory networks.…”

Members of BTB gene family regulate negatively nitrate uptake and nitrogen use efficiency in Arabidopsis thaliana and Oryza sativa

“…We recently showed Ca 2+ act as a second messenger in the nitrate signaling pathway (Riveras et al, 2015). Calciumdependent protein kinases are key elements of nitrate signaling including CIPK8, a regulator of primary nitrate-responsive genes , and CIPK23, a kinase that phosphorylates the NPF6.3/NRT1.1 nitrate transceptor (Ho et al, 2009).…”