Caren Chang Lab
Ethylene hormone signaling
ACC signaling: the case for a novel plant hormone
Plants hormones such as ethylene control many aspects of plant biology. The small molecule 1-aminocyclopropane-1-carboxylic acid (ACC) is well-known as the precursor in ethylene biosynthesis. Compelling new data from our lab suggests that ACC itself is a signaling molecule that impacts plant growth and development distinctly from ethylene (unpublished). Moreover, this signal appears to have evolutionarily predated the ability of higher land plants to efficiently convert ACC to ethylene. We are studying the role of ACC as a signaling molecule and investigating its signaling pathway using evolutionarily relevant model species, including Arabidopsis thaliana, Marchantia polymorpha (liverwort) and Physcomitrella patens (moss).
Our prior work on the cloning and characterization of the ethylene receptor gene led to the conclusion that the ethylene receptor gene has a plastid origin. Other than this, there is little known about the evolution of the ethylene signaling pathway in land plants. Using high throughput transcriptomics in collaboration with the lab of Charles Delwiche (UMD), we identified evolutionarily relevant species of Charophycean algae (freshwater green algae) that carry homologs of ethylene signal transduction. Our study of the function of these homologs in ethylene signaling and the identification of an ethylene response in Spirogyra pratensis suggested that ethylene has been conserved as a plant hormone over 450 million years (Ju et al., Nature Plants 1: Article 14004 doi:10.1038/nplants.2014.4; Van de Poel et al., Plant Physiol. 172: 533-545. doi:10.1104/pp.16.00299 ).
Evolution of ethylene signaling and response
Green algae Spirogyra (photo by Dr. Bram Van de Poel)
Function of EIN2, a central regulator in ethylene signaling
EIN2, a central regulator of ethylene signaling, is localized to the ER membrane. We discovered that EIN2 is phosphorylated by the CTR1 protein kinase in the absence of ethylene (Ju et al., PNAS 109:19486-19491, 2012). When ethylene is present, the receptors inactivate CTR1 and consequently the EIN2 C-terminal signaling domain is cleaved and translocates to the nucleus. Once in the nucleus, the transcription factors EIN3 and EIL1 are activated. We have been investigating the function of the EIN2 N-terminal domain, which has similarity to the Nramp family of metal ion transporters.
Figure 4 from Ju et al., PNAS, 2012)
Proteomic responses to ethylene
In collaboration with Dr. Bret Cooper (USDA-ARS, Beltsville MD), we have used mass spectrometry to detect ethylene-induced post-translational responses, such as changes in protein abundance or phosphorylation, in various cellular compartments (e.g., Chen et al., Mol. BioSyst. 7:2637-2650, 2011). Such changes will lead to the identification of proteins involved in ethylene signaling and response at a global level in plant and algal species.