CIPK23 is involved in iron acquisition of Arabidopsis by affecting ferric chelate reductase activity

Abstract

Iron deficiency is one of the major limiting factors affecting quality and production of crops in calcareous soils. Numerous signaling molecules and transcription factors have been demonstrated to play a regulatory role in adaptation of plants to iron deficiency. However, the mechanisms underlying the iron deficiency-induced physiological processes remain to be fully dissected. Here, we demonstrated that the protein kinase CIPK23 was involved in iron acquisition. Lesion of CIPK23 rendered Arabidopsis mutants hypersensitive to iron deficiency, as evidenced by stronger chlorosis in young leaves and lower iron concentration than wild-type plants under iron-deficient conditions by down-regulating ferric chelate reductase activity. We found that iron deficiency evoked an increase in cytosolic Ca(2+) concentration and the elevated Ca(2+) would bind to CBL1/CBL9, leading to activation of CIPK23. These novel findings highlight the involvement of calcium-dependent CBL-CIPK23 complexes in the regulation of iron acquisition. Moreover, mutation of CIPK23 led to changes in contents of mineral elements, suggesting that CBL-CIPK23 complexes could be as "nutritional sensors" to sense and regulate the mineral homeostasis in Arabisopsis.

A laboratory simulation of Arabidopsis seed dormancy cycling provides new insight into its regulation by clock genes and the dormancy‐related genes DOG1, MFT, CIPK23 and PHYA

“…This protein forms a calcium‐sensing complex with CBL1 or CBL9 (CALCINEURIN B‐LIKE PROTEIN), which is involved in iron, nitrate and potassium transport and sensing (Léran et al . ; Manik et al ; Tian et al ). Its role in regulating nitrate transport and signalling by the NITRATE TRANSPORTER 1.1 (NRT1.1) transceptor (duel nutrient transport/signalling function) and the crucial role this plays in the regulation of ABA levels in seeds is well characterized (reviewed in Finch‐Savage and Footitt ).…”

“…Here, Col‐0 and cipk23 lose light but not nitrate sensitivity during induction of secondary dormancy suggesting that loss of nitrate sensitivity is related to NRT1.1 protein levels and the action of factors such as DOG1 that regulate deep dormancy (reviewed in Finch‐Savage and Footitt ). CIPK23‐CBL complexes also have other functions, for example, as nutrient sensors to monitor mineral homeostasis in general (Tian et al ). Further work is therefore needed to fully understand the role of CIPK23 in dormancy regulation.…”

Advances and current challenges in calcium signaling

“…In contrast to AKT1/AtKC1 (Arabidopsis K + Channel 1) and HAK5 potassium uptake systems a single nitrate ‘transceptor’ CHL1 (NRT1.1; Nitrate transporter 1.1; NPF6.3) mediates both high‐affinity and low‐affinity nitrate uptake depending on its phosphorylation status at threonine residue 101 mediated by CIPK23 (Liu & Tsay, ; Léran et al ., ). In addition, it was recently shown that CIPK23 activates iron transport in Arabidopsis roots but inhibits AMT1;2 (ammonium transporter 1;2) mediated NH 4 + uptake in Arabidopsis roots to avoid toxic accumulation of cytoplasmic ammonium (Tian et al ., ; Straub et al ., ) (Fig. ).…”

“…Tansley review New Phytologist activates iron transport in Arabidopsis roots but inhibits AMT1;2 (ammonium transporter 1;2) mediated NH 4 + uptake in Arabidopsis roots to avoid toxic accumulation of cytoplasmic ammonium (Tian et al, 2016;Straub et al, 2017) (Fig. 1).…”

The combination of K+ deficiency with other environmental stresses: What is the outcome?

“…Interestingly, CIPK23 regulates the acquisition of other nutrients. The NH 4 + transporters AMT1;1 and AMT1;2 are inactivated by CIPK23‐mediated phosphorylation at high NH 4 + concentrations, avoiding toxic NH 4 + accumulation (Straub et al ), and the CBL1/CBL9‐CIPK23 complexes are also involved in Fe acquisition by affecting ferric chelate reductase activity (Tian et al ). In conclusion, CIPK23 emerges as an interesting hub for general plant nutrition.…”