AtCIPK16 Mediates Salt Stress Through Phytohormones and Transcription Factors

Abstract

Soil salinity causes large productivity losses for agriculture worldwide. "Next-generation crops" that can tolerate salt stress are required for the sustainability of global food production. Previous research in Arabidopsis thaliana aimed at uncovering novel factors underpinning improved plant salinity tolerance identified the protein kinase AtCIPK16. Overexpression of AtCIPK16 enhanced shoot Na + exclusion and increased biomass in both Arabidopsis and barley. Here, a comparative transcriptomic study on Arabidopsis lines expressing AtCIPK16 was conducted in the presence and absence of salt stress, using an RNA-Seq approach, complemented by AtCIPK16 interaction and localisation studies. We are now able to provide evidence for AtCIPK16 activity in the nucleus. Moreover, the results manifest the involvement of a transcription factor, AtTZF1, phytohormones and the ability to quickly reach homeostasis as components important for improving salinity tolerance in transgenics overexpressing AtCIPK16. Furthermore, we suggest the possibility of both biotic and abiotic tolerance through AtCIPK16, and propose a model for the salt tolerance pathway elicited through AtCIPK16. PrxR) (Baxter et al. 2014; Mittler et al. 2011); c) osmotic adjusters that can maintain low intracellular osmotic potential in plants under salt stress (for example proline, glycine betaine, free amino acids, sugars, polyamines and polyphenols) (Rosa et al. 2009); d) phytohormones that can facilitate a broad array of adaptive responses and long distance signalling (such as abscisic acid, indole acetic acid, cytokinins, gibberellic acid, salicylic acid, brassinosteroids, jasmonates, ethylene) (Fahad et al. 2015; Peleg and Blumwald 2011; Ryu and Cho 2015); and e) salt sensors including those that sense cytosolic Ca 2+ changes resulting from changes in the cytosol due to salinity and communicate the effects to downstream activating proteins (calcineurin-B-like proteins; CBLs and CBL-interacting protein kinases; CIPKs, calcium-dependent protein kinases; CDPKs, calmodulins; CaMs, calmodulin-like proteins; CAMLs, etc.) (Shabala et al. 2015).

AtCIPK16, a CBL-interacting protein kinase gene, confers salinity tolerance in transgenic wheat

“…Osmotic adjusters including glycine, betaine, polyphenol, sugars, proline, free amino acids, and polyamines have the ability to maintain low intracellular osmotic potential under salt stress in plants. Phytohormones like abscisic acid, cytokinin, gibberellic acid, brassinosteroids, jasmonates, indole acetic acid, and ethylene facilitate a broad array of adaptive responses and signaling in response to salt stress ( Shabala et al., 2015 ; Amarasinghe et al., 2020 .…”

“…A sum of 10 loci encoding CBLs and 26 CIPKs encoding loci was found in A. thaliana , 10 CBLs and 34 CIPKs were determined in rice ( O. sativa ), 9 CBLs and 14 CIPKs were reported in barley ( Hordeum vulgar e), 7 CBLs and 13 CIPKs were demonstrated in soybean ( Glycine max ), and 2 CBLs and 7 CIPKs were identified in pine ( Pinus ) ( Ma et al., 2020 ; Tong et al., 2021 ; Xiaolin et al., 2022 ). Arabidopsis thaliana CIPKs ( CIPK1 , CIPK3 , CIPK6 , CIPK8 , CIPK16 , CIPK21 , CIPK23 , and CIPK24 ) had been known to be involved in salinity tolerance in plants ( Amarasinghe et al., 2020 ; Ding et al., 2022 ). In the wheat genome, approximately 24 CBL and 79 CIPK genes had been identified ( Ma et al., 2020 ).…”

“…Sensors (CBLs/Ca 2+ -binding domains) phosphorylate AtCIPK16 to relieve it from autoinhibition to further phosphorylate multiple downstream targets. In A. thaliana , AtCIPK16 was reported to possess a strong affinity with CBL4 and CBL5 rather than with CBL1, CBL2, CBL9, and CBL10 ( Amarasinghe et al., 2020 ). AtCIPK16 has also been constitutively overexpressed in a barley cultivar (Golden promise) and reported to improve salinity tolerance with a 20%-45% increase in plant biomass compared with traditional breeding.…”

“…Osmotic adjusters including glycine, betaine, polyphenol, sugars, proline, free amino acids, and polyamines have the ability to maintain low intracellular osmotic potential under salt stress in plants. Phytohormones like abscisic acid, cytokinin, gibberellic acid, brassinosteroids, jasmonates, indole acetic acid, and ethylene facilitate a broad array of adaptive responses and signaling in response to salt stress (Shabala et al, 2015;Amarasinghe et al, 2020. Salt stress creates depolarization of the plasma membrane due to Na + entry into the cell and initiates the outward potassium ion (K + ) current to repolarize the plasma membrane potential. After repolarization of the plasma membrane with activation of the H + pump by the phosphorylation process, the calcium ion (Ca 2+ ) homeostasis is restored and potassium ion (K + ) efflux channels are closed (Boudsocq and Sheen, 2013;Van Kleeff et al, 2018).…”