Evolutionary conservation and downstream interactions of PHYTOCHROME KINASE SUBSTRATEs in phototropism
Year: 2026
Type: dissertation
Abstract: Plants need to optimize the amount of photosynthetically active light they can capture. One of the ways they achieve this is through changing the direction of their growth towards the light. This happens specifically in unfavourable light conditions, such as etiolated seedlings in darkness or seedlings growing under vegetative shade. A gradient of blue light is perceived across the hypocotyl by phototropins, which leads to lateral auxin asymmetry. Decreased auxin concentration on the lit side reduce cell elongation, while increased auxin concentration on the shaded side enhanced elongation. This produces a bending of the hypocotyl towards the source of blue light. How phototropin signalling leads to the auxin asymmetry is unknown. Phototropins are located at the plasma membrane of the cell, and interact there with several proteins critical for phototropic signalling: NPH3, RPT2 and the PHYTOCHROME KINASE SUBSTRATEs (PKSs). Using the grass Brachypodium distachyon, we show that both the subcellular localisation and phototropic function of PKS4 is conserved between monocots and dicots. Additionally, we studied differences in the recently diverged PKS1 and 2. Our results indicate that in a limited evolutionary timespan multiple part of the protein changed, creating differences in their roles in phototropism. PKSs are intrinsically disordered proteins that rely on conserved motifs (A-G) to function. PKS4 motif D is central to the phototropic function of PKS4, yet its function is unknown. Here, we show that BTB/POZ MATH DOMAIN 4 interacts with PKS4 motif D to slow down phototropism in seedlings growing in true shade. We find that the established SBC-like motif is not needed for interaction with the BPM4 MATH domain, and that the interaction does not lead to PKS4 degradation. The PHOTOREGULATORY PROTEIN KINASEs (PPKs) are another protein family potentially interacting with PKS4 motif D. On the one hand, PPK triple mutants show some phototropism phenotypes and PPK4 interacts with PKS4 motif D in yeast. On the other hand, results on PPK subcellular localisation were inconclusive and the PPK mutant phenotype is highly pleiotropic. Therefore, it remains uncertain if PPKs have a direct role in phototropism.
Source: IRIS
Language: English
Topic: Light effects on plants
Subfield: Plant Science
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W7221432633