Mostafa Abdelrahman, Rie Nishiyama, Cuong Duy Tran, Miyako Kusano, Ryo Nakabayashi, Yozo Okazaki, Fumio Matsuda, Ricardo A. Chávez Montes, Mohammad Golam Mostofa, Weiqiang Li, Yasuko Watanabe, Atsushi Fukushima, Maho Tanaka, Motoaki Seki, Kazuki Saito, Luis Herrera-Estrella, and Lam-Son Phan Tran

PNAS November 30, 2021 118 (48) e2105021118

Significance

The regulatory roles of cytokinin (CK) signaling on metabolic plasticity of plant response to salt stress remain widely unknown. A comprehensive metabolome and transcriptome analysis of CK-signaling–defective Arabidopsis thaliana histidine-containing phosphotransfer protein ahp2,3,5 and type-B Arabidopsis response regulator arr1,10,12 triple mutants under nonsaline and saline conditions revealed that CK signaling induces a reprogramming of gene-to-metabolite networks involved in Arabidopsis response to salinity. CK signaling modulates prestress and poststress accumulations of sugars, amino acids, and anthocyanins as well as membrane lipid reprogramming as an emerging mechanism of salinity adaptation in Arabidopsis. Our results provide insights into CK-signaling–mediated regulation of gene-to-metabolite networks in response to salt stress, enabling the efficient application of CK biology in stress tolerance-oriented plant biotechnology.

Abstract

Cytokinin (CK) in plants regulates both developmental processes and adaptation to environmental stresses. Arabidopsis histidine phosphotransfer ahp2,3,5 and type-B Arabidopsis response regulator arr1,10,12 triple mutants are almost completely defective in CK signaling, and the ahp2,3,5 mutant was reported to be salt tolerant. Here, we demonstrate that the arr1,10,12 mutant is also more tolerant to salt stress than wild-type (WT) plants. A comprehensive metabolite profiling coupled with transcriptome analysis of the ahp2,3,5 and arr1,10,12 mutants was conducted to elucidate the salt tolerance mechanisms mediated by CK signaling. Numerous primary (e.g., sugars, amino acids, and lipids) and secondary (e.g., flavonoids and sterols) metabolites accumulated in these mutants under nonsaline and saline conditions, suggesting that both prestress and poststress accumulations of stress-related metabolites contribute to improved salt tolerance in CK-signaling mutants. Specifically, the levels of sugars (e.g., trehalose and galactinol), amino acids (e.g., branched-chain amino acids and γ-aminobutyric acid), anthocyanins, sterols, and unsaturated triacylglycerols were higher in the mutant plants than in WT plants. Notably, the reprograming of flavonoid and lipid pools was highly coordinated and concomitant with the changes in transcriptional levels, indicating that these metabolic pathways are transcriptionally regulated by CK signaling. The discovery of the regulatory role of CK signaling on membrane lipid reprogramming provides a greater understanding of CK-mediated salt tolerance in plants. This knowledge will contribute to the development of salt-tolerant crops with the ability to withstand salinity as a key driver to ensure global food security in the era of climate crisis.

See: https://www.pnas.org/content/118/48/e2105021118

Fig. 3.

Heatmap hierarchical clustering and genotype–genotype correlations of 83 metabolites differentially produced in ahp2,3,5 and arr1,10,12 mutants, relative to WT plants, grown under nonsaline (ahp2,3,5-C/WT-C and arr1,10,12-C/WT-C) and saline (ahp2,3,5-S/WT-S and arr1,10,12-S/WT comparisons) conditions. (A–E) Heatmap hierarchical clusters of sugars (A), amino acids and polyamines (B), lipids and sterols (C), flavonoids, phenolics, and glucosinolates (D), and other general metabolites (E) in the investigated comparisons. (F) Genotype–genotype correlations based on the Pcc of DPMs in the investigated comparisons. The metabolite production levels in the heatmaps are a z-score–normalized data matrix. Red and blue colors indicate increased and decreased levels of metabolites, respectively, as indicated by the colored scales.