Arabidopsis thaliana
has five ethylene hormone receptors, which bind ethylene and elicit responses critical for plant growth and development. Here we describe a negative regulator of ethylene responses,
REVERSION-TO-ETHYLENE SENSITIVITY1
(
RTE1
), which regulates the function of at least one of the receptors,
ETR1
, in
Arabidopsis
.
RTE1
was identified based on the ability of
rte1
mutations to suppress ethylene insensitivity of the dominant gain-of-function allele
etr1-2
.
rte1
loss-of-function mutants have an enhanced ethylene response that closely resembles the
etr1
null phenotype. The
etr1 rte1
double null mutant is identical to the
etr1
and
rte1
single null mutants, suggesting that the two genes act in the same pathway.
rte1
is unable to suppress the
etr1-1
gain-of-function allele, placing
RTE1
at or upstream of
ETR1
.
rte1
also fails to suppress gain-of-function mutations in each of the four other ethylene receptor genes.
RTE1
encodes a previously undescribed predicted membrane protein, which is highly conserved in plants and protists but absent in fungi and prokaryotes. Ethylene treatment induces
RTE1
expression, and overexpression of
RTE1
confers reduced ethylene sensitivity that partially depends on
ETR1
. These findings demonstrate that
RTE1
is a negative regulator of ethylene signaling and suggest that
RTE1
plays an important role in
ETR1
function.
Ethylene is an important plant growth regulator perceived by membrane-bound ethylene receptors. The ETR1 ethylene receptor is positively regulated by a predicted membrane protein, RTE1, based on genetic studies in Arabidopsis. RTE1 homologs exist in plants, animals and protists, but the molecular function of RTE1 is unknown. Here, we examine RTE1 expression and subcellular protein localization in order to gain a better understanding of RTE1 and its function in relation to ETR1. Arabidopsis plants transformed with the RTE1 promoter fused to the b-glucuronidase (GUS) reporter gene revealed that RTE1 expression partly correlates with previously described sites of ETR1 expression or sites of ethylene response, such as the seedling root, root hairs and apical hook. RTE1 transcript levels are also enhanced by ethylene treatment, and reduced by the inhibition of ethylene signaling. For subcellular localization of RTE1, a functional RTE1 fusion to red fluorescent protein (RFP) was expressed under the control of the native RTE1 promoter. Using fluorescence microscopy, RTE1 was observed primarily at the Golgi apparatus and partially at the endoplasmic reticulum (ER) in stably transformed Arabidopsis protoplasts, roots and root hairs. Next, a functional ETR1 fusion to a 5xMyc epitope tag was expressed under the control of the native ETR1 promoter. Immunohistochemistry of root hairs not only showed ETR1 residing at the ER as previously reported, but revealed substantial localization of ETR1 at the Golgi apparatus. Lastly, we demonstrated the subcellular co-localization of RTE1 and ETR1. These findings support and enhance the genetic model that RTE1 plays a role in regulating ETR1.
SummaryEthylene is an important regulator of plant growth, development and responses to environmental stresses. Arabidopsis perceives ethylene through five homologous receptors that negatively regulate ethylene responses. RTE1, a novel gene conserved in plants, animals and some protists, was recently identified as a positive regulator of the ETR1 ethylene receptor. Here, we genetically analyze the dependence of ETR1 on RTE1 in order to obtain further insight into RTE1 function. The function of RTE1 was found to be independent and distinct from that of RAN1, which encodes a copper transporter required for ethylene receptor function. We tested the ability of an rte1 loss-of-function mutation to suppress 11 etr1 ethylene-binding domain mis-sense mutations, all of which result in dominant ethylene insensitivity due to constitutive signaling. This suppression test uncovered two classes of etr1 mutations -RTE1-dependent and RTE1-independent. The nature of these mutations suggests that the ethylene-binding domain is a possible target of RTE1 action. Based on these findings, we propose that RTE1 promotes ETR1 signaling through a conformational effect on the ethylene-binding domain.
The plant growth regulator ethylene is perceived by a family of homologous receptors that negatively regulate ethylene responses. It is well established that dominant missense mutations within the ethylene-binding domain of any of these receptors result in ethylene insensitivity (Chang et al
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.