Enhanced ethylene responsiveness in the Arabidopsis eer1 mutant results from a loss‐of‐function mutation in the protein phosphatase 2A A regulatory subunit, RCN1

Abstract

SummaryEthylene signaling in Arabidopsis begins with a family of ®ve ethylene receptors that regulate the activity of the Raf-like kinase, CTR1. Recent work to identify novel factors required for modulating ethylene signaling resulted in the isolation of enhanced ethylene response 1 (eer1), a mutant that displays both increased sensitivity and increased amplitude of response to ethylene. Molecular cloning of eer1 reveals that its mutant phenotype results from a loss-of-function mutation in the previously characterized RCN1, one of three PP2A A regulatory subunits in Arabidopsis. Our analysis shows that neither RCN1 expression nor PP2A activity is regulated by ethylene. Instead, we found that Arabidopsis PP2A-1C, a PP2A catalytic subunit previously characterized as interacting with RCN1, associates strongly with the kinase domain of CTR1 in vitro. This likely represents a role for PP2A in modulation of CTR1 activity because an in vitro kinase assay did not reveal phosphorylation of either RCN1 or PP2A-1C by CTR1, indicating that neither of them is a substrate for CTR1. PP2A activity is required for Ras-dependent activation of mammalian Raf, with reductions in PP2A activity signi®cantly compromising the effectiveness of this mechanism. Our genetic and biochemical results suggest that a similar requirement for PP2A activity exists for ethylene signaling, with loss-of-function mutations affecting PP2A activity possibly reducing the effectiveness of CTR1 activation, thus lowering the threshold required for manifestation of ethylene response.

A protein phosphatase 2A complex spatially controls plant cell division

“…PP2AA1 is considered to have a cardinal role in seedlings. Although morphologically similar to the wild type, PP2AA1 mutants display abnormal ethylene and ABA responses, as well as perturbed polar auxin transport [22][23][24][25] . PP2AA2 and PP2AA3 functions are unmasked only in a pp2aa1 mutant background 25 and neither pp2aa2 and pp2aa3 mutant nor pp2aa2-a3 double mutant plants have altered morphological phenotypes per se (see ref.…”

Ethylene Insensitivity Conferred by theGreen-ripeandNever-ripe 2Ripening Mutants of Tomato

“…EIR1 functions as an auxin transporter and may be a target for ethylene regulation of auxin transport to mediate gravitropic responses in the root (Luschnig et al, 1998). The eer1 mutant results from a loss-of-function mutation in the protein phosphatase 2A A regulatory subunit, RCN1 (Larsen and Cancel, 2003). This gene has also been implicated in regulating auxin responses in roots and abscisic acid signaling in guard cells (Garbers et al, 1996;Kwak et al, 2002) Figure 5.…”

“…Subsequent biochemical characterization indicated that the PP2A catalytic subunit, PP2A-1C, interacts with the kinase domain of CTR1 but is not a phosphorylation substrate of CTR1. These findings led the authors to postulate that PP2A activity may modulate ethylene responses by altering CTR1 activity (Larsen and Cancel, 2003).…”

Modulation of Ethylene Responses Affects Plant Salt-Stress Responses

“…The ETR1 receptor function can be regulated by RTE1 or the copper transporter RAN1 Resnick et al, 2006). ETR1 and ERS1 can interact with CTR1 that may be modulated by protein phosphatase 2A (Clark et al, 1998;Gao et al, 2003;Larsen and Cancel, 2003). Homologous genes of ethylene receptors have been isolated from many other plants, e.g.…”