Towards consolidating a mechanism whereby light signalling modulates microtubules dynamics

ARICO DENISE; DIEGO WENGIER; BURASCHICK; LUCIANA CASTRO; MAZZELLA AGUSTINA

Exposición; RAFV; 2021

PhosphoryIation events provide a powerful mechanism of transducing light signals. In an early light-induced phosphoproteome study in Arabidopsis thaliana, we identified a protein that presents light-responsive dephosphorylation in the presence of photoactivated photoreceptors. This protein was previously reported to interact with the key repressor of photomorphogenesis COP1 and thus, it is potentially involved in early photomorphogenesis events. In vivo assays with transcriptional reporters presented the expression pattern in dark-grown seedlings; comprising cotyledons, upper hypocotyl and roots. GUS assays, RT-qPCR and translational reporters with native promoter revealed that light downregulates its expression. Several confocal microscopy assays with stably transgenic over-expressing lines showed localization to cortical microtubules. Indeed, the C-terminal domain containing the light-regulated phosphosite is necessary for microtubule association. We are studying the biological implications of this phosphosite by generating phospho-mimic/dead transgenic lines. Going further in post-translational regulation, treatments with MG132 suggested some partitioning between microtubules and nucleus when blocking proteasome activity in the light. To confirm this, we are currently generating the over-expressing lines in background cop1-6. Finally, it is known that photomorphogenic inhibition of growth is stronger in the upper one-half of the Arabidopsis hypocotyl, which is where light-signalling mutant hypocotyls are found to continue to elongate. As microtubules are key regulators of cell expansion and the upper hypocotyl is the more light-sensitive region of this embryonic shoot; we are evaluating phenotypes of CRISPR-CAS9 mutated lines regarding growth and microtubule dynamics. All these results lead to a model that links the light-signalling pathway to microtubules regulation.