Depending on dynamics and amplitude of temperature changes there can be different pathways for the signalling of temperature stress. Cold, for example, is signalled differently when temperature drops rapidly versus gradually. In the latter case, it was known that components of the circadian clock (namely, RVE4 and RVE8) are involved in signalling. These activate the primary regulators of cold responses, the DRE-binding protein 1/C-repeat binding factors (DREB1/CBF) transcription factors. Because RVE4 and RVE8 also activate heat-responsive genes at high temperatures, it was hypothesized that other factors are responsible for conferring promoter specificity under low or high temperatures. LNKs are known coactivators of RVEs and are thus good candidates for this role. Arabidopsis has four paralogue LNKs. LNK1 and LNK2 interact with RVE4 and RVE8 and are required for transcriptional coactivation of core clock genes, but less is known about the other paralogues (LNK3 and LNK4).
The researchers found that expression of all four LNK paralogues is induced under cold stress, but expression of LNK3 and LNK4 is more strongly induced than expression of LNK1 and LNK2. Overexpression of LNK3 and LNK4, but not LNK1 and LNK2, can further increase cold-induced DREB1 expression compared to the overexpression of RVE8, which suggests that LNK3 and LNK4 may confer cold specificity. Consequently, lnk34 double mutants — but not lnk12 double mutants — showed reduced DREB1 expression under cold stress. On the other hand, heat-inducible expression of the ETHYLENE RESPONSIVE FACTORS ERF53 and ERF54 is attenuated in the lnk12 double mutant but not the lnk34 double mutant. Finally, it was found that LNK3 and LNK4 are specifically phosphorylated under cold stress. Thus, LNKs may have diversified to convey different temperature signals to RVEs and direct them to the corresponding target genes.
This is a preview of subscription content, access via your institution