Forisome

{{Use dmy dates|date=April 2022}} '''Forisomes''' are proteins occurring in the sieve tubes of Fabaceae. They are synthesised in companion cells and later moved to sieve elements where they are surrounded by other micro and macro molecules.<ref name="Srivastava2015">{{cite journal |last1=Srivastava |first1=Vineet Kumar |title=Calcium-energized motor protein forisome controls damage in phloem: potential applications as biomimetic ''smart'' material |journal=Critical Reviews in Biotechnology |date=June 2015 |volume=35 |issue=3 |pages=401–413 |doi=10.3109/07388551.2013.823598 |pmid=24020505 |url=https://doi.org/10.3109/07388551.2013.793181 |access-date=18 April 2026|url-access=subscription }}</ref> Forisomes are 10–55 μm long and 1–5 μm wide.<ref name="Noll2022">{{cite journal |last1=Noll |first1=Gundula |title=Guardians of the phloem – forisomes and beyond |journal=The New Phytologist |date=2022 |volume=236 |issue=4 |pages=1245–1260 |doi=10.1111/nph.18476 |pmid=36089886 |bibcode=2022NewPh.236.1245N |url=https://nph.onlinelibrary.wiley.com/doi/full/10.1111%2Fnph.18476 |access-date=4 April 2026|url-access=subscription }}</ref> They expand and contract anisotropically in response to changes of electric field, pH, or concentration of Ca²⁺ ions. Unlike most other moving proteins, the change is not dependent on ATP. Forisomes function as valves in sieve tubes of the phloem system, by reversibly changing shape between low-volume ordered crystalloid spindles and high-volume disordered spherical conformations. The change from ordered to disordered conformation can increase the protein's volume by three to ninefold,<ref name="Noll2022"/> cause loss of birefringence present in the crystalline phase, and induce a 120% radial expansion and 30% longitudinal shrinkage. In ''Vicia'' it was shown that forisomes are associated to the endoplasmic reticulum at sieve plates. There are evidences that the forisomes's behavior could depend on Ca²⁺ changes provoked by Ca²⁺-permeable ion channels, located on the endoplasmic reticulum and plasma membrane of sieve elements.<ref name="Furch">{{cite journal |title= Sieve Element Ca²⁺ Channels as Relay Stations between Remote Stimuli and Sieve Tube Occlussion in ''Vicia faba''|author1=Alexandra C.U. Furch |author2=Aart J.E. van Bel |author3=Mark D. Fricker |author4=Hubert H. Felle |author5=Maike Fuchs |author6=Jens Hafke |year= 2009 |journal= The Plant Cell |volume= 21 |pages= 2118–2132 |pmc=2729599 |pmid=19602624 |doi=10.1105/tpc.108.063107 |issue=7|bibcode=2009PlanC..21.2118F }}</ref> responsible for shape changes.

==Etymology== The name ''forisome'', coined by Knoblauch<ref name="Srivastava2015"/>, is derived from the Latin words ''foris'' meaning outside and gate and ''soma'' meaning body. Together, the names refer to its behavior as an opening body, going from a compact conformation, to an open, dispersed conformation in order to temporarily block the flow of assimilates in the phloem after taking damage from phloem feeding pests and other wounding.<ref name="Noll2022"/>

==Functions in the phloem== The phloem is often at risk of attack from herbivores and phloem feeding pests that want the sugars it transports. Forisomes act as a defense mechanism in the phloem of leguminous plants and enact sieve element occlusion at damage sites by rapidly changing conformation to enlarge its size and stop the outflow of phloem sap and prevent infection from phytopathogens.<ref name="Noll2022"/>

==Activation of forisomes== Forisome activation is initially caused by a stress to the phloem with some being mechanical disturbances such as feeding by insects or herbivory, or exposure to environmental factors like radiation or heat shock.<ref name="Walker2022"/> Stressors are then sensed by mechanoreceptors and ligand-activated or voltage-gated channels,<ref name="Srivastava2015"/> all signaling for an influx of calcium. Ca²⁺ influx into the sieve element triggers the disordered form of the Forisome. Forisomes do not need to be synthesized upon wounding because they are always present in the sieve element.<ref name="Srivastava2014">{{cite journal |last1=Srivastava |first1=Vineet Kumar |title=Calcium powered phloem protein of SEO gene family "Forisome" functions in wound sealing and act as biomimetic smart materials |journal=Plant Signaling & Behavior |date=2014 |volume=9 |issue=9 |article-number=e29438 |doi=10.4161/psb.29438 |pmid=25763691 |pmc=4205131 |bibcode=2014PlSiB...9E9438S }}</ref> Forisomes have also been shown to be ATP independent as they are able to undergo conformation change when exposed to Ca²⁺ in vitro.<ref name="Noll2011">{{cite journal |last1=Noll |first1=Gundula A |title=Native and artificial forisomes: functions and applications |journal=Applied Microbiology and Biotechnology |date=2011 |volume=89 |issue=6 |pages=1675–1682 |doi=10.1007/s00253-011-3117-6 |pmid=21286708}}</ref> Interactions between the negative residues of forisomes and the positive Ca²⁺ are responsible for the activating the dispersed form.<ref name="Srivastava2014"/><ref name="Knoblauch2014">{{cite journal |last1=Knoblauch |first1=Micheal |title=The structure of the phloem – still more questions than answers |journal=The Plant Journal |date=2012 |volume=70 |issue=1 |pages=147–156 |doi=10.1111/j.1365-313X.2012.04931.x |pmid=22449049 |bibcode=2012PlJ....70..147K }}</ref> While not practical in biological circumstances forisomes are also able to enter the dispersed conformation when in contact with other cations like Ba²⁺ and Sr²⁺.<ref name="Noll2011"/>

The binding mechanism and site of calcium in forisomes is yet to be identified with theories suggesting that the binding site for Ca²⁺ is multiple proteins long, making it difficult to detect the exact calcium binding motifs.<ref name="Srivastava2015"/> Upon phloem damage repair Ca²⁺ efflux initiates forisomes to reverse to a condensed conformation. Dissolution of forisomes occurs within 3-8 minutes, allowing phloem sap flow to resume.<ref name="Srivastava2014"/> Artificially produced forisomes have been shown to self-assemble into spindle-shaped structures and longitudinally arranged fibrils similar to natural forisomes, even outside of plant cells.<ref name="Srivastava2014"/> Forisomes' ability to self-assemble independent of their surroundings indicates that they are self-organizing proteins that do not require cellular machinery to form.<ref name="Srivastava2014"/>

Oxygen inhibits the return to the compact conformation of forisomes.<ref name="Noll2022"/> When wounding occurs within the phloem, an influx of oxygen keeps the forisomes locked in the dispersed conformation.<ref name="Noll2022"/> This suggests that an intact sieve element is necessary for the change from dispersed to condensed conformation in forisomes.<ref name="Noll2022"/>

==Structure== Forisomes are predominantly composed of alpha helical structures and contain negatively and positively charged amino acid residues.<ref name="Srivastava2015"/> Their electrostatic attractive nature likely contributes to the expansive and contractive properties of forisomes.<ref name="Srivastava2015"/> Forisomes function and general structure is well understood, but the precise molecular mechanisms such as how Ca²⁺ is sensed and controls conformations is incompletely understood.<ref name="Srivastava2015"/> Forisomes are able to undergo over 5,000 cycles of expansion and contraction in response to electro-titration.<ref name="Rose2010">{{cite journal |last1=Rose |first1=Judith |title=The Ca 2+ response of a smart forisome protein is dependent on polymerization |journal=Protein Science |date=2022 |volume=31 |issue=3 |pages=602–612 |doi=10.1002/pro.4256 |pmid=34897845 |pmc=8862433 }}</ref> Forisomes remain contracted at pH 4.9-9.0 and expand when at a pH below 4.9 and a pH above 9.0.<ref name="Tuteja2010">{{cite journal |last1=Tuteja |first1=Narendra |title=Forisomes: calcium-powered protein complexes with potential as 'smart' biomaterials |journal=Trends in Biotechnology |date=2010 |volume=28 |issue=2 |pages=102–110 |doi=10.1016/j.tibtech.2009.11.005 |pmid=20004992}}</ref> At pH 12 forisomes lose stability and undergo permanent denaturation.<ref name="Tuteja2010"/>

==Defense against phloem-feeding pests== Phloem feeding pests such as aphids, whiteflies, mealybugs, and more have large incentive to puncture the phloem and ingest the sugars present in phloem sap.<ref name="Walker2022">{{cite journal |last1=Walker |first1=G.P. |title=Sieve element occlusion: Interactions with phloem sap-feeding insects. A review |journal=Journal of Plant Physiology |date=2022 |volume=269 |page=15358 |article-number=153582 |doi=10.1016/j.jplph.2021.153582 |pmid=34953413 |bibcode=2022JPPhy.26953582W }}</ref> Sieve element defenses and phloem feeding pests are at a coevolutionary arms race where plants evolve defense mechanisms and phloem feeders evolve penetration mechanisms. One of the defense mechanisms in the sieve elements of the phloem is forisomes. Forisomes' expansion upon phloem damage is able to block phloem feeders from ingesting the sugars in the phloem. Aphids have evolved saliva that contains Ca²⁺ chelating properties allowing them to reverse expanded forisomes by lowering the amount of Ca²⁺ present.<ref name="Srivastava2015"/>

==Research and applications== Forisomes ability to be isolated from living tissues and to have its conformation changed with Ca²⁺ in vitro makes them have large research potential in nanotechnological settings.<ref name="TutejaHistory2010">{{cite journal |last1=Tuteja |first1=Narendra |title=Forisomes as calcium-energized protein complex: A historical perspective |journal=Plant Signaling & Behavior |date=2010 |volume=5 |issue=5 |pages=497–500 |doi=10.4161/psb.10985 |pmid=20215879 |pmc=7080470 |bibcode=2010PlSiB...5..497T }}</ref> The swelling and contracting nature of forisomes depending only on the presence of Ca²⁺ and other triggers that are independent of ATP has enabled use in biotechnological and microfluidic areas.<ref name="TutejaHistory2010"/> Prototype valve systems using forisomes in liquid flowing microchannels have demonstrated an ability to reversibly control the flow of liquid based on divalent cations and change in Ph.<ref name="Noll2011"/> In microfluidic devices forisomes high hydraulic resistance makes it possible for technical devices to be sealed efficiently.<ref name="Noll2011"/>

Forisomes have potential to be unique proteins machines that are different from other protein-based molecular machines that require ATP to supply unidirectional force.<ref name="Noll2011"/> Biological motor functions such as actin–myosin and kinesin/dynein–microtubule systems require ATP to create unidirectional force.<ref name="Noll2011"/> Different to those motor functions, forisomes create bidirectional force and do not use ATP.<ref name="Noll2011"/> This creates new possibilities for microscale and nanoscale machines with concept designs such as microgrippers and synthetic muscle being proposed.<ref name="Noll2011"/>

==References== {{reflist}}

==External links== * [http://www.ipam.ucla.edu/abstract/?tid=5939&pcode=CMWS2 Forisome: A smart plant protein inside a phloem system] * [http://faculty.washington.edu/amyshen/smartsystem.pdf Forisome based biomimetic smart materials] {{Webarchive|url=https://web.archive.org/web/20160314214809/http://faculty.washington.edu/amyshen/smartsystem.pdf |date=14 March 2016 }} * [http://www.medgadget.com/archives/2006/12/forisome_protein.html Forisome Protein, a Key to Biomimetic Materials] {{Webarchive|url=https://web.archive.org/web/20070928162137/http://www.medgadget.com/archives/2006/12/forisome_protein.html |date=28 September 2007 }}

Category:Motor proteins Category:Smart materials Category:Plant proteins