FIGURE 4.

Summary of shade and warm temperatures sensing mechanisms. The photoconversion of phytochromes is dependent on temperature. Both high temperature and a low red to far-red photon ratio will promote the conversion from the active (PHYB-Pfr) to the inactive (PHYB-Pr) PHYB from. This releases PHYB-mediated repression of PIFs, which can then activate their targets. PIFs activities are, nevertheless, regulated spatially and temporally at diverse levels: transcriptionally by transcription factors such as ELF3 and HY5 and post-transcriptionally by interactors preventing its binding to DNA sequences. PIF4 interacts with ARF6 and BZR1 in the BAP module to regulate cell elongation. In normal conditions, all of these factors are bound and inhibited by DELLA proteins. High temperature and shade also increase GA levels leading to the degradation of the DELLAs and the activation of PIFs and their partners. The binding of PIFs to their targets is regulated by the presence of proteins that compete for the same DNA binding sites and by the chromatin state at their promoters. Once activated PIFs will induce the expression of regulatory genes as well as the production of auxin leading ultimately to an appropriate developmental response.