Cytokinin
Cytokinin is a plant hormone that regulates cell division, meristem activity, vascular development, leaf senescence, nutrient responses, and stress adaptation[1]. Mechanistically, cytokinin signaling proceeds through a His-Asp phosphorelay in which AHK2, AHK3, and AHK4/CRE1 receptors transmit signals through AHP proteins to ARR transcriptional regulators[2]. In Arabidopsis, receptor-mutant studies show that AHK2, AHK3, and AHK4 control shoot growth, leaf senescence, seed size, germination, root development, and cytokinin metabolism[3]. Compared with related receptor isoforms, AHK3 has a distinct role in cytokinin-mediated leaf longevity through phosphorylation of ARR2[4]. In disease models, cytokinin-activated ARR2 promotes immunity against Pseudomonas syringae through TGA3/NPR1-dependent salicylic acid signaling[5]. In tomato, cytokinin response induces systemic immunity, modulates LeEIX2 pattern-recognition receptor trafficking, and promotes resistance to fungal pathogens[6]. For experimental applications, receptor-level antagonists such as PI-55 and S-4893 help dissect cytokinin perception and cytokinin signaling specificity[7][8].
References:
- [1]. Hwang I, et al. Cytokinin signaling networks. Annu Rev Plant Biol. 2012;63:353-80. [Content Brief]
- [2]. Müller B, et al. Arabidopsis cytokinin signaling pathway. Sci STKE. 2007 Oct 9;2007(407):cm5. [Content Brief]
- [3]. Riefler M, et al. Arabidopsis cytokinin receptor mutants reveal functions in shoot growth, leaf senescence, seed size, germination, root development, and cytokinin metabolism. Plant Cell. 2006 Jan;18(1):40-54. [Content Brief]
- [4]. Kim HJ, et al. Cytokinin-mediated control of leaf longevity by AHK3 through phosphorylation of ARR2 in Arabidopsis. Proc Natl Acad Sci U S A. 2006 Jan 17;103(3):814-9. [Content Brief]
- [5]. Choi J, et al. The cytokinin-activated transcription factor ARR2 promotes plant immunity via TGA3/NPR1-dependent salicylic acid signaling in Arabidopsis. Dev Cell. 2010 Aug 17;19(2):284-95. [Content Brief]
- [6]. Gupta R, et al. Cytokinin response induces immunity and fungal pathogen resistance, and modulates trafficking of the PRR LeEIX2 in tomato. Mol Plant Pathol. 2020 Oct;21(10):1287-1306. [Content Brief]
- [7]. Spíchal L, et al. The purine derivative PI-55 blocks cytokinin action via receptor inhibition. FEBS J. 2009 Jan;276(1):244-53. [Content Brief]
- [8]. Kanno Y, et al. Comprehensive hormone profiling in developing Arabidopsis seeds: examination of the site of ABA biosynthesis, ABA transport and hormone interactions. Plant Cell Physiol. 2010 Dec;51(12):1988-2001. [Content Brief]
