Phototropin Interactions with SUMO Proteins.

Justyna Łabuz,Aneta Bażant,Dominika Jagiełło-Flasińska,Paweł Hermanowicz,Aleksandra Giza,Filip Bartnicki,Ewa Sitkiewicz,Agnieszka Katarzyna Banaś,Wojciech Strzałka,Hanna Lasok,Halina Gabryś,Olga Sztatelman,Weronika Krzeszowiec,Anna Kozłowska

doi:10.1093/pcp/pcab027

Abstract

The disruption of the sumoylation pathway affects processes controlled by the two phototropins (phots) of Arabidopsis thaliana, phot1 and phot2. Phots, plant UVA/blue light photoreceptors, regulate growth responses and fast movements aimed at optimizing photosynthesis, such as phototropism, chloroplast relocations and stomatal opening. Sumoylation is a posttranslational modification, consisting of the addition of a SUMO (SMALL UBIQUITIN-RELATED MODIFIER) protein to a lysine residue in the target protein. In addition to affecting the stability of proteins, it regulates their activity, interactions and subcellular localization. We examined physiological responses controlled by phots, phototropism and chloroplast movements, in sumoylation pathway mutants. Chloroplast accumulation in response to both continuous and pulse light was enhanced in the E3 ligase siz1 mutant, in a manner dependent on phot2. A significant decrease in phot2 protein abundance was observed in this mutant after blue light treatment both in seedlings and mature leaves. Using plant transient expression and yeast two-hybrid assays, we found that phots interacted with SUMO proteins mainly through their N-terminal parts, which contain the photosensory LOV domains. The covalent modification in phots by SUMO was verified using an Arabidopsis sumoylation system reconstituted in bacteria followed by the mass spectrometry analysis. Lys 297 was identified as the main target of SUMO3 in the phot2 molecule. Finally, sumoylation of phot2 was detected in Arabidopsis mature leaves upon light or heat stress treatment.

Highlights

Phototropins are plant blue/UVA photoreceptors, which control growth responses and fast movements, such as stomatal opening and chloroplast relocations (Christie 2007, Banas et al 2012)
Chloroplast movements and phototropism were examined in Arabidopsis SUMO mutants: sum1, sum2, sum3 and sum5 and E3 ligase mutants: siz1 and mms21
Our microscopic observations indicate that the dark positioning of chloroplasts in palisade cells is not affected by the mutation in the SIZ1 gene (Fig. 1E)

Summary

Introduction

Phototropins (phots) are plant blue/UVA photoreceptors, which control growth responses and fast movements, such as stomatal opening and chloroplast relocations (Christie 2007, Banas et al 2012). Two phot genes are found in the genome of Arabidopsis thaliana: PHOT1 (Liscum and Briggs 1995) and PHOT2 (Jarillo et al 2001, Kagawa 2001) They share highly redundant functions; phot is more sensitive to light than phot (Sakai et al 2001, Harada and Shimazaki 2007, Hart et al 2019). Both phots are responsible for phototropic bending (Sakai et al 2001) in seedlings. Gene expression is regulated by phots to a very small extent (Chen et al 2008, Lehmann et al 2011)

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Conclusion