Evolution of photoperiod sensing in plants and algae

E olu ion o pho ope iod sensing in plan s and algae Glo ia Se ano-Bueno * , F ancisco J Rome o-Campe o, E a Lucas- Reina *,** , Jose M Rome o and Fede ico Val e de Measu ing day leng h con e s a s ong i ness imp o emen o pho osyn he ic o ganisms as i allows hem o an icipa e ligh phases and ake he bes decisions p eceding diu nal ansi ions. In close associa ion wi h signals om he ci cadian clock and he pho o ecep o s, pho ope iodic sensing cons i u es also a p ecise way o de e mine he passing o he seasons and o ake annual decisions such as he bes ime o lowe o he beginning o do mancy. Pho ope iodic sensing in pho osyn he ic o ganisms is ancien and wo majo s ages in i s e olu ion could be iden i ied, he cyanobac e ial ime sensing and he e olu iona y ool ki ha a ose in g een algae and de eloped in o he pho ope iodic sys em o mode n plan s. The mos ecen disco e ies abou he e olu ion o he pe cep ion o ligh , measu emen o day leng h and ela ionship wi h he ci cadian clock along he e olu ion o he euka yo ic g een lineage will be discussed in his e iew. Add ess Plan De elopmen Uni , Ins i u e o Plan Biochemis y and Pho osyn hesis, CSIC-Uni e sidad de Se illa, 49 h, Ame ico Vespucio A ., 41092 Se illa, Spain Co esponding au ho : Val e de, Fede ico ([email p o ec ed]. es) In oduc ion Ea h o a ion a ound i s axis and a ound he sun p oduces p edic able day leng h (pho ope iod) changes h ough he seasons ha plan s use, ia sophis ica ed mechanisms, o measu e ime and ake c ucial physiological decisions [1]. Pho ope iodism, o he abili y o de ec day leng h, is p esen in ea ly pho osyn he ic euka yo es so ha algae can p oduce se e al pho ope iod esponses [2]. This way, du ing he g een lineage e olu ion, pho ope iodism pe aded in o he majo physiological sys ems, allowing hem o p edic he passing o he seasons and p epa e plan s o yea - ound p edic able changing condi ions. The pho ope iod sensing sys em in ol es a way o de ec ligh (pho o ecep o s) and an in e nal sys em o measu e ime (ci cadian clock). In ime hey became so impo an o unicellula ee li ing algae ha o some ma ine picoeuka yo es 90% o i s ansc ip ome is con olled by he clock [3]. Howe e , mo e e ol ed and lexible species like mode n plan s, which de eloped he capaci y o adap o di e en en i onmen s, ha e educed his numbe o less han 50% [4]. Pa adoxically, mo e in e - wined, complex sys ems allowed o a mo e independen esponse o ex e nal cues, hus pe mi ing he coloniza- ion o e e demanding new niches and he acquisi ion o no el and complex physiological unc ions [5]. Pho o ecep o s e olu ion Li ing o ganisms use a clus e o pho o ecep o s o mea- su e he quali y, quan i y and di ec ion o ligh o modu- la e physiological esponses o changing ligh s [6]. This is pa icula ly impo an o pho osyn he ic o ganisms ha equi e ligh ene gy o pho osyn hesis and consequen ly o g ow and de elop. Pho o ecep o s can be di ided in o h ee g oups acco ding o he ligh quali y hey de ec . Red and a - ed ligh s a e abso bed by phy och omes (PHYs) while h ee ypes o pho o ecep o s pe cei e he blue/UV-A: C yp och omes (CRYs), Pho o opins (PHOTs) and h ee plan -speci ic LOV/F-box/Kelch- epea p o eins ZEITLUPE (ZTL), FLAVIN-BIND- ING KELCH REPEAT F-BOX (FKF), and LOV KELCH REPEAT PROTEIN 2 (LKP2). Finally, UV RESISTANCE LOCUS 8 (UVR8) was ecen ly shown o be a UV-B pho o ecep o [7]. Excellen e iews on plan and algae pho o ecep o s uc u e and unc ion ha e ecen ly been published [8–13]. The speci ic pho o ecep o se has e ol ed ac oss pho o- syn he ic euka yo es (Figu e 1). In he chlo ophy e model alga Chlamydomonas einha d ii, UV-B ligh is de ec ed by UVR8 while blue/UV-A is de ec ed by one PHOT (pho1), wo DASH (D osophila, A abidopsis, Synechocys is and Human) CRYs, one plan -like CRY (pCRY) and one animal-like CRY (aCRY). The la e can espond bo h o blue and ed ligh [12,14  ,15]. In he e n Adian um capillus- ene is ou canonical plan PHYs ha e been ** P esen add ess: IHSM-UMA-CSIC, Depa amen o de Biologıı ´a Molecula y Bioquı ´mica, Uni e sidad de Ma ´laga, 29071 Ma ´laga, Spain. iden i ied, wo PHOTs and i e CRYs [16]. Fe ns include a speci ic neoch ome, a chime ic pho o ecep o consis ing o an N- e minus PHY domain and se e al C- e minus PHOT domains ha can sense bo h blue and ed/ a - ed ligh o egula e chlo oplas mo emen and pho o opism [6]. Howe e , UV-B pho o ecep o s ha e no been desc ibed in e ns, hei absence jus i ied by hei g ow h habi s unde low-ligh angiospe m canopies. In he model plan A abidopsis haliana, ed/ a - ed ligh s a e de ec ed by i e PHYs (A-E), blue/UV-A by wo PHOTs, h ee CRYs, and ZTL/FKF1/LKP2 p o eins [6,11,13], while UV-B by a canonical UVR8 (Figu e 1a). Inc ease in pho o ecep o s numbe and unc ion du ing plan e olu- ion has been ela ed o i ness imp o emen [9]. In plan s and algae, pho ope iod egula es a numbe o p ocesses including pho omo phogenesis, g ow h, lowe - ing, s ess ole ance and ci cadian hy hms [16,17,18  ]. In da kness, some o hese pa hways a e inhibi ed by CON- STITUTIVE PHOTOMORPHOGENIC 1 (COP1), a RING- inge E3 ubiqui in ligase. Du ing he day, COP1 is inhibi ed by he pho o ecep o s allowing he ac i a ion o pho ope iodic-dependen p ocesses (Figu e 1a). A nigh , COP1 in e ac ion wi h SUPPRESSOR OF PHY- TOCHROME A (SPA1) a ge s he ansc ip ion ac o s ELONGATED HYPOCOTYL 5 (HY5) and CON- STANS (CO) o ubiqui ina ion and deg ada ion, sup- p essing pho omo phogenesis and lowe ing espec i ely [20,21]. Pho oac i a ed CRY1, CRY2 and PHYA di ec ly bind SPA1 and inhibi he o ma ion o COP1-SPA1 complex [19]. PHYB also p omo es COP1-SPA1 dissoci- a ion and pho omo phogenic de elopmen [22]. COP1 in e ac ion wi h EARLY FLOWERING 3 (ELF3) induces deg ada ion o GIGANTEA (GI), a ci cadian clock associa ed p o ein, p ocess inhibi ed by CRY1/ CRY2 in blue ligh [23]. Upon UV-B i adia ion, UVR8 Figu e 1 C PHO1 C CRY dash C CRY dash C CRYa C CRYp UVR8 PHO1 PHO2 CRY1 CRY2 CRY DASH FKF1 ZTL LKP2 PHYB PHYA PHYE PHYD PHYC COP1 CO GIHY5 COP1 HY5 UV-B ole ance Pho o- mo phogenesis Flowe ing Ci cadian hy hm C UVR8 C COP1 C HY5 UV-B ole ance C COP1 C CO S a ch bios yn e sis Cell cycle (a) (b) Cu en Opinion in Plan Biology Ligh signal ansduc ion and pho ope iodic egula ion by COP1 in A. haliana (a) and C. einha d ii (b). In A. haliana, pho oac i a ed CRY1, CRY2, PHYA and PHYB inhibi COP1 allowing accumula ion o e ec o s and esul ing in he speci ic ligh esponses. Unde UV-B, COP1 ac s as posi i e egula o ac i a ing, among o he s, UVR8, HY5 and consequen ly up egula ing UV-B ole ance genes. UV-B signal ansduc ion is conse ed in C. einha d ii, al hough C HY5 implica ion has no been in es iga ed (dash lines). A ows indica e posi i e egula ion, while ba s ep esen nega i e egula ion. Low le els o C CO exp ession obse ed in c c ya mu an sugges a conse ed CRY- COP1-CO pa hway, al hough C COP1 implica ion has no been desc ibed (dash lines). Pho o ecep o s no in ol ed in COP1 egula ion a e shown in g ey. PRR9, PRR7 and PRR5 p esen a se ies o successi e exp ession peaks a ea ly mo ning, mid-day and a e noon espec i ely (Figu e 2c) and hei p o ein p oduc s bind o he same posi ions a he CCA1 p omo e whe e a G-box can be ound, ep essing i s exp ession du ing he en i e day, and comple ing he posi i e/nega i e eedback mo ning loop [31]. TOC1 (PRR1) is di ec ly ep essed by CCA1 using he e ening elemen loca ed in i s p omo e . TOC1 in u n also ac s as a ep esso o CCA1 o ming he cen al nega i e eedback loop [31]. PRRs homologues ha e been iden i- ied in all plan axa. A single PRR gene was iden i ied in he O. au i genome (O TOC1) p esen ing a simila exp es- sion p o ile as TOC1 and PRR5 (Figu e 2c) and symme ic o he one in O CCA1, sugges ing ha he cen al loop was al eady es ablished in algae and is conse ed ac oss he en i e euka yo ic g een lineage [29  ]. Addi ionally, an e ening elemen has been ound in he p omo e o O TOC1 p o iding suppo ing e idence. None o he wo PRRs iden i ied in Chlamydomonas ollow simila exp ession p o iles o any o he PRRs in A abidopsis, which sugges s a di e gen e olu ion in Chlamydomonas in he egula ion o ci cadian hy hms [32]. Fou di e en PRRs we e ound in he Physcomi ella (a moss ha seems o ha e de i ed om he di ec e olu iona y line o mode n plan s) genome. All hese genes exhibi he same exp es- sion pa e n, peaking a dusk wi h hei oughs a dawn. No di e si ica ion in hei peaking ime poin s like he A abidopsis PRR9/7/5 is obse ed, possibly because hese genes a e he esul o e y ecen duplica ion e en s [33]. The hi d eedback loop is called he e ening loop whe e TOC1 also plays a key ole oge he wi h GI and ZTL (Figu e 2). Bo h genes ha e been shown o be ansc ip- ionally co- egula ed di ec ly by CCA1, PRRs and TOC1 [27  ,31,34  ]. In u n, GI and ZTL a e known o o m a complex in ol ed in blue ligh and empe a u e sensing ha induces TOC1 deg ada ion by he 26S p o easome [35]. I is ele an o no e ha A abidopsis ZTL homo- logue, FKF1, oge he wi h GI, media es CYCLING DOF FACTORs (CDFs) deg ada ion and he subse- quen CO ac i a ion [36], a connec ion be ween he ci cadian clock and pho ope iodic lowe ing. No po en ial GI homologue has been iden i ied in mic oalgae and Physcomi ella, bu i is p esen in o he b yophy es such as Ma chan ia o Selaginella and he seed plan s Picea and O yza, sugges ing ha his gene is exclusi e o land plan s [33]. GI plays also a c ucial ole in he empe a u e compensa ion o he A abidopsis ci cadian clock [37] and he de ec in empe a u e compensa ion obse ed in Physcomi ella clock has been asc ibed o he absence o GI [33]. ZTL p esen s h ee di e en p o ein domains: N- e minal LOV in ol ed in blue ligh sensing, F-box ha media es p o ein ubiqui ina ion, and mul iple C- e minal Kelch domains in ol ed in p o ein in e ac ions. Simila o GI, ZTL homologs ha e only been iden i ied in monome izes and in e ac s wi h COP1, p omo ing he exp ession o HY5, which is esponsible o ac i a ion o UV-B esponsi e genes [24]. In Chlamydomonas cells g own unde blue ligh , C CO (Chlamydomonas CO homo- log [18  ]) ansc ip le els a e lowe ed in he c c ya mu an [15], sugges ing a possible C CO ac i a ion by C CRYa. Besides, UV-B pe cep ion and signalling in Chlamydomo- nas is media ed by C UVR8 ha in e ac s wi h C COP1, al hough C HY5 implica ion has no been demons a ed [14  ]. RING- inge E3 ligases homologues o COP1 can be also ound in o he mic oalgae. The e o e, i seems ha a cen al ole o COP1-like signalling mechanisms was al eady es ablished in chlo ophy es and e ol ed o he complexi y ound in mode n plan s. Ci cadian clocks in algae and plan s Ci cadian clocks a e molecula mechanisms ha gene a e hy hmic o oscilla ing signals wi h a pe iod o app oxi- ma ely 24 hou s. They a e ubiqui ous sys ems p esen in almos all euka yo ic o ganisms, bu in spi e o he long e olu iona y dis ance among hem, hey a e composed o s ikingly simila gene ne wo ks comp ising in e wined posi i e and nega i e eedback loops [25]. These genes a e no always o hologues, sugges ing a con e gen and independen e olu iona y his o y. Recen ly, high h oughpu sequencing and genome-wide phylogene ics a e s a ing o un eil an in e es ing e olu ion o he gene ne wo k unde pinning he ci cadian clock composi ion in he g een lineage. Th ee in e locked eedback loops ha e been iden i ied in he model species A abidopsis; mo ning, cen al and e en- ing loops (Figu e 2a) [26]. The key gene in he mo ning loop is CIRCADIAN CLOCK-ASSOCIATED 1 (CCA1) ha codes o a MYB ansc ip ion ac o [27  ] wi h a con- se ed N- e minal SHAQKYF mo i (Figu e 2b). MYB amily has gone h ough an in ense p ocess o ampli ica- ion and unc ional di e si ica ion in he g een lineage [28] and CCA1 homologues a e p esen in e e y plan axa, om he single copy gene O CCA1 in Os eococcus [29  ] o he la ge gene amily in A abidopsis including CCA1, LATE ELONGATED HYPOCOTYL (LHY) and REV- EILLE (RVE) 4, 6 and 8 [30]. All hese homologues, wi h he excep ion o Chlamydomonas, exhibi he same exp es- sion pa e n as A abidopsis CCA1: A peak a dawn and a ough a dusk (Figu e 2c). ChIP-seq da a has shown ha CCA1 binds di ec ly o he p omo e s o he o he key genes in he mo ning loop, he PSEUDO-RESPONSE REGULATOR 9, 7 and 5 (PRR9/7/ 5) ecognizing a speci ic DNA sequence called e ening elemen [27  ] (Figu e 2a). PRRs a e ep esso s ha con ain in hei N- e minus a ecei e -like domain (RLD) simila o he one in RESPONSE REGULATORS in ol ed in he His-Asp phospho elay sys em, while in he C- e mi- nus hey p esen a CO, COL1 and TIME OF CAB EXPRESSION 1 (TOC1) domain (CCT). In A abidopsis Figu e 2 (a) (b) (c) Mo ning Loop Cen al Loop E ening Loop PRR 5/7/9 CCA1/LHY TOC1 ZTL GI LUX RLD RLD wi h DDK mo i CCT SHAQKYF Myb LOV Fbox Kelch GARP Myb No malized Gene Exp ession No malized Gene Exp ession No malized Gene Exp essio No malized Gene Exp essio A abidopsis haliana Os eococcus au i Os eococcus au i Physcomi ella pa en s TOC1 PRR5 PRR7 PRR9 ZTO ZT2 ZT4 ZT6 ZT8 ZT10 ZT12 ZT14 ZT16 ZT18 ZT20 ZT22 ZT24 ZTO ZT2 ZT4 ZT6 ZT8 ZT10 ZT12 ZT14 ZT16 ZT18 ZT20 ZT22 ZT24 ZTO ZT2 ZT4 ZT6 ZT8 ZT10 ZT12 ZT14 ZT16 ZT18 ZT20 ZT22 ZT24 ZTO ZT2 ZT4 ZT6 ZT8 ZT10 ZT12 ZT14 ZT16 ZT18 ZT20 ZT22 ZT24 O CCA1 O TOC1 CCA1 A abidopsis haliana O yza sa i a Picea abies Selaginella moellendo ii Chlamydomonas einha d ii AT5G24470 AT2G46830 AT1G01060 AT5G61380 AT5G57360 AT2G18915 AT1G22770 AT3G46640 AT5G02810 AT2G46790 Os03g17570 Os08g06110 Os02g40510 Os02g05700 Os06g47890 Os01g08700 Os01g74020 Os11g05930 MA_71728g0010 MA_115536g0010 MA_71728g0010 MA_70291g0010MA_10427223g0010 MA_3352g0010 15421531 15422641 15415582 15403652 15410828 Pp3c16_18610 Pp3c3_37540 Pp3c16_18460 Pp3c15_13960 Pp3c4_2590 3 Pp3c25_4920 Pp3c25_5040 C e16.g676421 C e12.g514400 O 06g01320 O 13g01890 O 12g01470 C e02.g094150 C e10.g430750 Cu en Opinion in Plan Biology E olu ion o ci cadian clocks om algae o plan s. (a) T ansc ip ional ne wo k unde pinning he ci cadian clock in A abidopsis haliana based on occupancy p o iling by high h oughpu sequencing o ChIP-seq o CCA1, TOC1, PRR5, PRR7 and PRR9. Th ee di e en loops a e iden i ied, he mo ning loop cons i u ed by CCA1 and PRR9/7/5, Howe e , he e a e di e se and speci ic pho ope iodic lowe ing egula o y s a egies. In he sho day (SD) plan ice, CO homologue unc ions as an inhibi o in LD and ac i a o in SD [45], while ano he COL sup- p esses lowe ing ega dless o day leng h [46]. In Med- icago and pea, CO seems o ha e no signi ican e ec in lowe ing ime and speci ically in he la e , FT exp ession is con olled solely by a CDF gene [47,48]. None heless, e olu ion goes e en u he , al e ing lowe ing ime a he species le el by na u al a ia ion in he cis- egula o y elemen s o he CO p omo e [49  ]. Mo eo e , a local adap a ion o eco ypes o di e en lowe ing s a egies depending on hei geog aphic loca ion has been desc ibed [50]. These examples and o he s [51–54] show how plan s ha e adap ed o op imize hei ep oduc i e iming. Al hough he belie ha CO is a widesp ead cen al elemen in he angiospe ms lowe ing pa hway is gene - a ing con o e sy [47,55  ], he GI-CDFs-CO-FT co e is highly conse ed among dis an ly ela ed lowe ing plan s. In ac , i has been shown ha COLs and DOFs egula o s ha e coe ol ed om single common algal ances o s, ollowing he inno a ion, ampli ica ion and di e gence model o gene e olu ion by duplica ion [56]. C. einha d ii is conside ed o be he ep esen a i e species o his common ances o , in which, a single copy gene o CO (C CO) ha con ols he exp ession o a single copy DOF (C DOF) has been cha ac e ized [18  ,57  ]. C CO is a cen al hub in ol ed in key physiological p ocesses such as ca bon me abolism and cell cycle, so ha i s exp ession is con olled by pho ope iod and i s mu a ion se e ely e ec s he capaci y o he algae o syn hesize s a ch and o synch onize cell di ision and g ow h [18  ,56]. Fu he mo e, C DOF induces, unlike A abidopsis, C CO exp ession in SD by di ec binding o i s p omo e . Howe e , in LD, i ep esses cell cycle p og ession in a C CO-independen way [57  ] (Figu e 3). Su p isingly, bo h genes phenocopied i s homologue unc ions in A abidopsis when ec opically exp essed; C CO inducing lowe ing ime while C DOF delays i [18  ,57  ]. Cu iously, COL1 (which sha es 80% amino acid simila i y wi h CO) o e exp ession p oduces no change in lowe ing ime and his migh e eal ano he e olu iona y aspec : I mus be he e ia y s uc u e o he algal p o eins wha is conse ed and ecognized by he plan egula o y mechanisms o emula e i s plan homologue unc ion [56]. This does no seem o be an isola ed e en because a simila case was obse ed when oma o CDFs we e exp essed in A abidopsis [58]. land plan s, al hough he h ee domains o ZTL ha e been sepa a ely iden i ied in di e en p o eins in Physco-mi ella, so ha hese p o eins could o m a complex unc ionally equi alen o ZTL [33]. Al e na i ely, a close inspec ion o he RLD domains in he PRR genes in Physcomi ella and Os eococcus has e ealed a po en ial phosphoacep o DDK mo i ha is no p esen in he PRRs o land plan s. This could indica e ha hese PRRs o m pa o a His -Asp phospho elay sys em. In ac , His idine kinases con aining an N- e minal LOV domain has been iden i ied in Os eococcus whe e i has been shown o espond o blue ligh , bind la in and ha e a ci cadian unc ion [38]. The e o e, hese LOV-HKs could possibly ake he ole o ZTL in Physcomi ella, Chlamy- domonas and Os eococcus. The e ening loop includes also LUX ARRHYTHMO, ELF3 and ELF4 ha ep ess ci cadian genes nigh exp ession [39]. LUX homologs ha e been ound in all plan axa examined bu no unc ional cha ac e iza ion is desc ibed. Po en ial ELF3/4 o hologues ha e been iden- i ied in Physcomi ella [33] and o he land plan s [40] bu he e seem o be no o hologues in Chlamydomonas [41] o Os eococcus. The e o e, i seems ha he cen al CCA1/LHY and TOC1 loop was es ablished e y ea ly in mic oalgae and he subsequen loops and addi ional con- ol le els ook place du ing he cou se o he e olu ion o land plan s. This way, he mo e complex he clock, he mo e esponses can be ex ac ed om i o con ol new physiological p ocesses, such as he abo e men ioned empe a u e compensa ion exe ed by GI [33]. This could explain how land plan s acqui ed a much mo e e sa ile con ol o he ex e nal condi ions, enhancing hei plas ici y and capaci y o colonize new ae ial niches. E olu ion o he pho ope iod pa hway The long day (LD) A. haliana plan and i s pho ope iodic con ol o lowe ing ime has been he model o day leng h sensing s udies. In A abidopsis CO p o ein ep e-sen s a cen al hub ha con ols lowe ing in he p ope season (Figu e 3, igh ). B ie ly, CO exp ession is egu-la ed by ci cadian clock and pho ope iodic inpu s h ough GI-FKF1, he CDFs and FLOWERING BHLHs (FBHs). CO p o ein s abili y is con olled by pho o e-cep o s, E3 ubiqui in ligases [42] and h ough he in e -ac ion wi h o he p o eins [43,44]. These complex egu-la o y laye s allow he co ec exp ession o he lo igen FLOWERING LOCUS T (FT) gene ha p omo es lowe ing. (Figu e 2 Legend Con inued) he cen al loop wi h TOC1 and CCA1 and inally, he e ening loop o med by TOC1, GI, ZTL and LUX. (b) Iden i ica ion o o hologues ci cadian clock p o eins in di e en plan axa including gene ID om speci ic da abases. No ice how p o eins in he mo ning and cen al loops a e conse ed ac oss he en i e g een lineage, while he key p o eins in he e ening loop, ZTL and GI, a e only p esen om Selaginella on. P o ein domains (RLD, CCT, Myb, LOV, Fbox and Kelch) a e colo -coded iden i ied on he able on he le . (c) Conse a ion o he exp ession p o iles o CCA1, PRR9/7/5 and TOC1 om A abidopsis haliana (le ) and O CCA1 and O TOC1 om Os eococcus au i ( igh ) in 24 hou s expe imen s a 12 hou s ligh /12 hou s da k pho ope iod. CCA1 and O CCA1 p esen simila exp ession p o iles peaking a dawn wi h a ough a dusk. O TOC1 and TOC1 exhibi simila exp ession pa e ns peaking a dusk wi h a ough a dawn. In ascula plan s, a g ea numbe s o DOFs and COLs unc ions ha e been inhe i ed om hei common ances- o . Fo example, CO igge s s a ch biosyn hesis and he DOF ansc ip ion ac o OBP1 con ols cell cycle [59,60]. So, no only DOF-CO module has coe ol ed, bu also a se o genes o key egula o y ne wo ks associa ed o hese genes. Addi ionally, COLs and DOFs ha e acqui ed, h oughou e olu ion, a wide epe oi e o plan -speci ic ligh -dependen unc ions [5,61,62] leading o mo e com- plex o ganism wi h a highe pho ope iod plas ici y. Discussion O e e olu iona y ime, pho osyn he ic o ganisms ha e lea n o li e and ex ac in o ma ion om pe iodic changes in sunligh [1,2]. As he complexi y o o ganisms inc eased, so did hei capaci y o espond o he en i- onmen and pa adoxically, o become mo e independen om i s igou s and mo e p ecise a aking c ucial li e decisions, such as he bes ime o he yea o lowe o he bes ime o he day o g ow. The massi e amoun o in o ma ion a ising om compa a i e genomics p ojec s is allowing us o unde s and pho ope iodic sensing wi h an e olu iona y pe spec i e. Acknowledgemen s The au ho s would like o hank unding om p ojec s BIO2011-28847- C02-00 and BIO2014-52425-P (Spanish Minis y o Economy and Compe i i eness, MINECO) pa ially suppo ed by FEDER unding. Re e ences and ecommended eading Pape s o pa icula in e es , published wi hin he pe iod o e iew, ha e been highligh ed as:  o special in e es  o ou s anding in e es 1. Lage c an z U: A he end o he day: a common molecula mechanism o pho ope iod esponses in plan s. J. Exp. Bo . 2009, 60:2501-2515. Figu e 3 Common ances o DOFs SD LD Cell cycle COLs Flowe ing S a ch byosin hesis S a ch byosin hesis S em elonga ion Bud Do mancy Tube g ow h Cell cycle G ow h egula o C:N me abolism Lipid me abolism Seed de elopemen Lipid me abolism Ni ogen me abolism Response o ligh s imulus ... ... ... C CO FT CO PHYB PHYA FBHs CDFs HOS1 COP1 CRY2 C DOF FBHCOP1HOS1 FT GI GI FKF1 Cu en Opinion in Plan Biology E olu ion o he pho ope iod pa hway elemen s om a common ances o . In A abidopsis ( igh ) he main elemen s o lowe ing pho ope iod pa hway a e shown. G ey and pu ple p o eins ep esen phy oc omes and E3 ubiqui ine ligase p o eins, espec i ely. S aigh and dash a ows show ansc ip ional and pos - ansc ip ional egula ion, espec i ely. Colo ed ci cles ep esen ligh quali y. In Chlamydomonas (le ) C CO and C DOF a e he i s known elemen s in ol ed in pho ope iodic signaling ( he e is no e idence o GI and FT p o eins p esence in g een algae). 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