Elucidating the role and function of Sensitive to Freezing6 (SFR6) and its interacting proteins in the control of stress tolerance

Abstract

The plant mediator transcriptional co-activator complex consists of in the region of 34 protein subunits that collectively link promoter-bound transcription factors with the activity of RNA polymerase II. Among them, Mediator subunit 16 (MED16; also known as SENSITIVE TO FREEZING6, SFR6) plays a major role in regulating the expression of specific genes in response to a variety of stresses including cold, drought, UV and pathogen infection. The structure of plant mediator has been hypothesised to be similar to that of yeast mediator but has not yet been proven.
Considering the structure of the yeast mediator complex, in which MED14, MED16 and MED2 occupy positions in the so-called “tail”, we would predict a close physical interaction between MED14, MED2 and MED16 in the plant complex. Therefore, this study investigated whether MED2 and MED14 control the same regulons as controlled by MED16. Results showed the necessity of these two proteins, like MED16, in gene regulation under cold, drought, and UV stresses and revealed a clear correlation between reduced levels of tolerance and impaired gene expression under cold and UV but not drought.
To investigate whether particular domains within MED16 might be responsible for the activation of specific genes under different stresses, complementation experiments were used to test the ability of three different truncated MED16 versions to restore cold-, dark- and UV-inducible expression. Some truncated versions were able to complement the mutant but the degree of complementation varied amongst transgenic lines.
Experiments were conducted to study the function of KIN10, an interacting protein of MED16 that appears to play a role similar to MED16 in regulation of stress genes and tolerance. The necessity of KIN10 in the control of a subset of the stress-inducible genes controlled by MED16 was demonstrated. Co-immunoprecipitation experiments revealed that regions within the N-terminal part of MED16 are essential for interaction with KIN10.