Functional analysis of AHK1/ATHK1 and cytokinin receptor histidine kinases in response to abscisic acid, drought, and salt stress in Arabidopsis.

In plants, multistep component systems play important roles in signal transduction in response to environmental stimuli and plant growth regulators. Arabidopsis contains six nonethylene receptor histidine kinases, and, among them, AHK1/ATHK1, AHK2, AHK3, and CRE1 were shown to be stress-responsive, suggesting their roles in the regulation of plant response to abiotic stress. Gain- and loss-of-function studies in Arabidopsis indicated that AHK1 is a positive regulator of drought and salt stress responses and abscisic acid (ABA) signaling.

Arabidopsis AtMYC2 (bHLH) and AtMYB2 (MYB) function as transcriptional activators in abscisic acid signaling.

In Arabidopsis, the induction of a dehydration-responsive gene, rd22, is mediated by abscisic acid (ABA). We reported previously that MYC and MYB recognition sites in the rd22 promoter region function as cis-acting elements in the drought- and ABA-induced gene expression of rd22. bHLH- and MYB-related transcription factors, rd22BP1 (renamed AtMYC2) and AtMYB2, interact specifically with the MYC and MYB recognition sites, respectively, in vitro and activate the transcription of the beta-glucuronidase reporter gene driven by the MYC and MYB recognition sites in Arabidopsis leaf protoplasts.

Isolation and functional analysis of a gene, tcsB, encoding a transmembrane hybrid-type histidine kinase from Aspergillus nidulans.

We cloned and characterized a novel Aspergillus nidulans histidine kinase gene, tcsB, encoding a membrane-type two-component signaling protein homologous to the yeast osmosensor synthetic lethal N-end rule protein 1 (SLN1), which transmits signals through the high-osmolarity glycerol response 1 (HOG1) mitogen-activated protein kinase (MAPK) cascade in yeast cells in response to environmental osmotic stimuli. From an A. nidulans cDNA library, we isolated a positive clone containing a 3,210-bp open reading frame that encoded a putative protein consisting of 1,070 amino acids.

Overexpression of Arabidopsis response regulators, ARR4/ATRR1/IBC7 and ARR8/ATRR3, alters cytokinin responses differentially in the shoot and in callus formation.

Arabidopsis ARR4/ATRR1/IBC7 and ARR8/ATRR3 are homologous genes of prokaryotic response regulators that are involved in the His-Asp phosphorelay signal transduction. We analyzed the function of these genes as response regulators using transgenic plants. Overexpression of ARR4 in cultured stems of the transgenics markedly promoted shoot formation in the presence of cytokinin, while overexpression of ARR8 repressed shoot formation and greening of calli.