Question

Explain the molecular aspects of hormonal regulation in ethylene; include terms such as proteasome and repressor, etc

In plant physiology

Answer 1

Ethylene is a principal signalling molecule in plants and is responsible for coordination of several responses including a multitude of biotic and abiotic stresses in plants.

At the level of transcription, ethylene induces transcription of several genes in response to a multitude of environmental and developmental stimuli. In order to understand, it is necessary to know how the hormone is synthesised and regulated and how the signal is transduced.

The main precursor for ethylene biosynthesis is S -adenosyl methionine which is an immediate precursor and is used as a substrate in several biochemical pathways. The first commited step of the pathway is the conversion of S - adenosyl methionine to 1 - amino cyclopropane carboxylic acid ( ACC ) by ACC synthase. ACC is then oxidised to ethylene by ACC oxidase. The rate - limiting step of this pathway is the first step of conversion of S - adenosyl methionine to ACC by ACS , which is encoded by a multigene family.  Phosphorylation of ACS2 and ACS6 by MPK6 (Mitogen-activated protein kinases 6) leads to the accumulation of ACS protein and, thus, elevated levels of cellular ACS activity and ethylene production. ETO1(ethylene-overproducing 1), in a gene that negatively regulates ACS activity and ethylene production. ETO1 also interacts with CUL3 (Cullin-dependent ubiquitin ligase 3), a constituent of ubiquitin ligase complexes, in which it is proposed that ETO1 serves as a substrate-specific adaptor protein. ETO1 thus has a dual mechanism, inhibiting ACS enzyme activity and targeting it for proteasome degradation. Therefore, this permits rapid modulation of the concentration of ethylene