Phototropin

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Phototropins are blue light photoreceptor proteins (more specifically, flavoproteins) that mediate phototropism responses across many species of algae, [1] fungi and higher plants. [2] Phototropins can be found throughout the leaves of a plant. Along with cryptochromes and phytochromes they allow plants to respond and alter their growth in response to the light environment. When phototropins are hit with blue light, they induce a signal transduction pathway that alters the plant cells' functions in different ways.

Contents

Phototropins are part of the phototropic sensory system in plants that causes various environmental responses in plants. Phototropins specifically will cause stems to bend towards light [3] and stomata to open. [4] In addition phototropins mediate the first changes in stem elongation in blue light prior to cryptochrome activation. [5] Phototropins are also required for blue light mediated transcript destabilization of specific mRNAs in the cell. [6]

Phototropins also regulate the movement of chloroplasts within the cell, [7] [8] notably chloroplast avoidance. It was thought that this avoidance serves a protective function to avoid damage from intense light, [9] however an alternate study argues that the avoidance response is primarily to increase light penetration into deeper mesophyll layers in high light conditions. [10] Phototropins may also be important for the opening of stomata. [11]

In green algae, Phototropins have been shown to be involved in process such as photoprotection [12] , starch metabolism [13] and phototactic behavior [14] . Even though some of the processes the algal phototropins affect are similar to those in plants, the mode of action differs in the different types of organisms. In general, light activation of algal photoropins cause major transcriptional changes of target genes [15] , which is not the case in plants [16] .

Enzyme activity

The crystal structure of the LOV2 domain of Phototropin-2 of Arabidopsis thaliana, generated using ChimeraX. Part of the LOV2 domain is hidden for clarity of the active site containing FMN. The dotted blue lines represent hydrogen bonds predicted as important in binding. In green are Cys426 and Arg427 residues which are crucial in photoactivity and FMN binding, respectively, with mutations resulting in total loss of function of the protein. Upon photoexcitation, the sulfur (yellow) of Cys426 forms a covalent bond with the carbon 4 of FMN. (PDBe: 4EEP) LOV2 domain of phototropin-2 protein from Arabidopsis thaliana.png
The crystal structure of the LOV2 domain of Phototropin-2 of Arabidopsis thaliana , generated using ChimeraX. Part of the LOV2 domain is hidden for clarity of the active site containing FMN. The dotted blue lines represent hydrogen bonds predicted as important in binding. In green are Cys426 and Arg427 residues which are crucial in photoactivity and FMN binding, respectively, with mutations resulting in total loss of function of the protein. Upon photoexcitation, the sulfur (yellow) of Cys426 forms a covalent bond with the carbon 4 of FMN. (PDBe: 4EEP)

Phototropins have two distinct light, oxygen, or voltage regulated domains (LOV1, LOV2) that each bind flavin mononucleotide (FMN). [18] The FMN is noncovalently bound to a LOV domain in the dark, but becomes covalently linked upon exposure to suitable light. [18] The formation of the bond is reversible once light is no longer present. [18] The forward reaction with light is not dependent on temperature, though low temperatures give increased stability of the covalent linkage, leading to a slower reversal reaction. [18]

Light excitation will lead to a conformational change within the protein, which allows for kinase activity. [19] There is also evidence to suggest that phototropins undergo autophosphorylation at various sites across the enzyme. [18] Phototropins trigger signaling responses within the cell, but it is unknown which proteins are phosphorylated by phototropins, or exactly how the autophosphorylation events play a role in signaling. [18]

Phototropins are typically found on the plasma membrane, but some phototropins have been found in substantial quantities on chloroplast membranes. [20] One study found that phototropins on the plasma membrane play a role in phototropism, leaf flattening, stomatal opening, and chloroplast movements, while phototropins on the chloroplasts only partially affected stomatal opening and chloroplast movement, [21] suggesting that the location of the protein in the cell may also play a role in its signaling function.

References

  1. ↑ Veetil, S.K; Mittal, C; Ranjan, P; Kateriya, S (July 2011). "A conserved isoleucine in the LOV1 domain of a novel phototropin from the marine alga Ostreococcus tauri modulates the dark state recovery of the domain" . Biochim Biophys Acta. 1810 (7): 675–82. doi:10.1016/j.bbagen.2011.04.008. PMID   21554927.
  2. ↑ Li, F. W., Rothfels, C. J., Melkonian, M., Villarreal, J. C., Stevenson, D. W., Graham, S. W., Wong, G. K. S., Mathews, S., & Pryer, K. M. (2015). The origin and evolution of phototropins. Frontiers in Plant Science, 6(AUG). https://doi.org/10.3389/fpls.2015.00637
  3. ↑ Price (2009). Molecular Basis of Botanical Biology. Phoenix Publishing. p. 213.
  4. ↑ Price (2009). Molecular Basis of Botanical Biology. Phoenix Publishing. p. 213.
  5. ↑ Folta, Kevin (2001). "Unexpected Roles for Cryptochrome 2 and Phototropin Revealed by High-resolution Analysis of Blue Light-mediated Hypocotyl Growth Inhibition". The Plant Journal. 26 (5): 471–78. doi: 10.1046/j.1365-313x.2001.01038.x . PMID   11439133.
  6. ↑ Brighton; et al. (2006). "Role of phototropin in the differential expression of blue light mediated mRNAs". International Journal of Molecular Botany. 72 (54): 672–691.
  7. ↑ Wada M, Kagawa T, Sato Y (2003). "Chloroplast movement". Annu Rev Plant Biol. 54 (1): 455–68. Bibcode:2003AnRPB..54..455W. doi:10.1146/annurev.arplant.54.031902.135023. PMID   14502999.
  8. ↑ DeBlasio SL, Luesse DL, Hangarter RP (September 2005). "A plant-specific protein essential for blue-light-induced chloroplast movements". Plant Physiol. 139 (1): 101–14. doi:10.1104/pp.105.061887. PMC   1203361 . PMID   16113226.
  9. ↑ Kasahara, M., Kagawa, T., Olkawa, K., Suetsugu, N., Miyao, M., & Wada, M. (2002). Chloroplast avoidance movement reduces photodamage in plants. Nature, 420(6917). https://doi.org/10.1038/nature01213
  10. ↑ Wilson, S., & Ruban, A. v. (2020). Rethinking the influence of chloroplast movements on non-photochemical quenching and photoprotection. Plant Physiology, 183(3). https://doi.org/10.1104/pp.20.00549
  11. ↑ Smith, Garland (2010). Fundamentals of Biomolecular Botany (2 ed.). Fisher Press. p. 340.
  12. ↑ Petroutsos, Dimitris; Tokutsu, Ryutaro; Maruyama, Shinichiro; Flori, Serena; Greiner, Andre; Magneschi, Leonardo; Cusant, Loic; Kottke, Tilman; Mittag, Maria; Hegemann, Peter; Finazzi, Giovanni; Minagawa, Jun (2016-09-22). "A blue-light photoreceptor mediates the feedback regulation of photosynthesis". Nature. 537 (7621): 563–566. doi:10.1038/nature19358. ISSN   0028-0836.
  13. ↑ Yuan, Yizhong; Iannetta, Anthony A.; Kim, Minjae; Sadecki, Patric W.; Arend, Marius; Tsichla, Angeliki; Águila Ruiz-Sola, M.; Kepesidis, Georgios; Falconet, Denis; Thevenon, Emmanuel; Tardif, Marianne; Brugière, Sabine; Couté, Yohann; Kleman, Jean Philippe; Sizova, Irina (2025-03-15). "Phototropin connects blue light perception to starch metabolism in green algae". Nature Communications. 16 (1). doi:10.1038/s41467-025-57809-3. ISSN   2041-1723. PMC   11909140 . PMID   40087266.
  14. ↑ Trippens, Jessica; Greiner, Andre; Schellwat, Jana; Neukam, Martin; Rottmann, Theresa; Lu, Yinghong; Kateriya, Suneel; Hegemann, Peter; Kreimer, Georg (November 2012). "Phototropin Influence on Eyespot Development and Regulation of Phototactic Behavior in Chlamydomonas reinhardtii". The Plant Cell. 24 (11): 4687–4702. doi:10.1105/tpc.112.103523. ISSN   1040-4651. PMC   3531860 . PMID   23204408.
  15. ↑ Huang, Kaiyao; Beck, Christoph F. (2003-05-13). "Phototropin is the blue-light receptor that controls multiple steps in the sexual life cycle of the green alga Chlamydomonas reinhardtii". Proceedings of the National Academy of Sciences. 100 (10): 6269–6274. doi:10.1073/pnas.0931459100. PMC   156361 . PMID   12716969.
  16. ↑ Ohgishi, Maki; Saji, Kensuke; Okada, Kiyotaka; Sakai, Tatsuya (2004-02-24). "Functional analysis of each blue light receptor, cry1, cry2, phot1, and phot2, by using combinatorial multiple mutants in Arabidopsis". Proceedings of the National Academy of Sciences. 101 (8): 2223–2228. doi:10.1073/pnas.0305984101. PMC   356932 . PMID   14982991.
  17. ↑ Łabuz, J., Sztatelman, O., & Hermanowicz, P. (2022). Molecular insights into the phototropin control of chloroplast movements. In Journal of Experimental Botany (Vol. 73, Issue 18). https://doi.org/10.1093/jxb/erac271
  18. 1 2 3 4 5 6 Łabuz, J., Sztatelman, O., & Hermanowicz, P. (2022). Molecular insights into the phototropin control of chloroplast movements. In Journal of Experimental Botany (Vol. 73, Issue 18). https://doi.org/10.1093/jxb/erac271
  19. ↑ Koyama, T., Iwata, T., Yamamoto, A., Sato, Y., Matsuoka, D., Tokutomi, S., & Kandori, H. (2009). Different role of the Jα helix in the light-induced activation of the LOV2 domains in various phototropins. Biochemistry, 48(32). https://doi.org/10.1021/bi9009192
  20. ↑ Kong, S. G., Suetsugu, N., Kikuchi, S., Nakai, M., Nagatani, A., & Wada, M. (2013). Both phototropin 1 and 2 localize on the chloroplast outer membrane with distinct localization activity. Plant and Cell Physiology, 54(1). https://doi.org/10.1093/pcp/pcs151
  21. ↑ Ishishita, K., Higa, T., Tanaka, H., Inoue, S. I., Chung, A., Ushijima, T., Matsushita, T., Kinoshita, T., Nakai, M., Wada, M., Suetsugu, N., & Gotoh, E. (2020). Phototropin2 contributes to the chloroplast avoidance response at the chloroplast-plasma membrane InterfAce1[CC-by]. Plant Physiology, 183(5). https://doi.org/10.1104/pp.20.00059

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