Arabidopsis LEAFY (LFY) gene and its homolog FLORICAULA (Flo) in Antirrhinum majus are homeotic genes encoding  plant specific helix-turn-helix transcription factor expressed at early stages of flower initiation (Anthony et al., 1993, Maizel et al., 2005). The floral fate of meristem induced by floral signals results in transcriptional activation of flower meristem identity genes LFY, APETALA1 (AP1) and CAULIFLOWER (CAL) at the shoot apex and their mutation results in shoot like structures instead of flowers (Weigel and Nilsson., 1995). The transition from inflorescence to floral meristem is induced by interaction of LFY with AP1. LFY RNA is strongly expressed in young flower primordia and  LFY might play a role in regulating other organ identity specifying homeotic genes AGAMOUS (AG) and APETALA3 (AP3), since its expression precedes the expression of AG and AP3 (Weigel et al., 1992). LFY belongs to the class of pioneer TFs  as it can access AP1 target region inside the nucleosome by displacing H1 linker histone and recruiting SWI/SNF chromatin remodelers resulting changes in chromatin accessibility  (Jin et al., 2021) and reprogramming roots cells to flower fate when ectopically expressed with WUSCHEL (homeodomain encoding TF) pluripotency factor (Gallois et al., 2004). Pioneer TFs functions in cell fate reprogramming and establishment of competence for changes in cellular fate (Zaret and Carroll., 2011). During vegetative phase, LFY is repressed by  TERMINAL FLOWER 1 (TFL1), a anti-florigen and  member of phosphatidylethanolamine-binding protein (PEBP) family acting as a transcriptional cofactor in floral repression complex consisting of FD, a bZIP TF. TFL1 is recruited by FD to the second exon of LFY. However in response to right cues, plants produce major PEBP family florigen FLOWERING LOCUS T (FT) and there is a competition between antagonist TFL1 and FT for chromatin bound FD at LFY locus. The florigen activation complex FT-FD act as a transient stimulus at target loci (Zhu et al., 2020). LFY consist of a highly conserved C-terminal DNA binding domain and a partially conserved proline rich N-terminal transcription activation domain and it activates gene expression by binding cooperatively as a dimer in a sequence specific manner to the pseudo-palindromic CCANTGT/G sequence in the promoter region of AP1 and AG target genes (Coen et al., 1990, Maizel et al., 2005, Hamès et al., 2008). RFL (Rice FLO/LFY), the FLO/LFY homolog of rice unlike FLO/LFY is expressed predominantly in panicle meristem and panicle branch primordia and its expression is greatly reduced in floral meristem thus implying its distinct role in panicle branching (Kyozuka et al., 1998). Based on RFL ectopic overexpression and knockdown in transgenic rice, it regulates flowering time activator gene OsMADS50 and plant architecture trait since RFL overexpression results in precocious flowering and reduction delays transition to flowering (Rao et al., 2008).

The ZFL1 (Zea FLO/LFY 1)  and ZFL2, FLO/LFY homologs in maize regulate flower and inflorescence patterning as transposon mediated mutation in these genes resulted in floral organ identity and pattern disruption, and defects in vegetative to reproductive phase transition and inflorescence architecture thus indicating their conserved role between monocots and dicots (Bomblies et al., 2003).  Based on a similar zfl1;zfl2 double mutant phenotype, these FLO/LFY homologs act as an upstream regulator of floral identity gene ABC. PpLFY1 and PpLFY2, FLO/LFY homologs in moss Physcomitrella patens regulate first mitotic cell division after zygote formation (Tanahashi et al., 2005). RT-PCR analysis indicated that WFL (Wheat FLO/LFY), wheat ortholog of FLO/LFY is involved in spikelet formation and plays a role in developing plea in the wheat floret (Shitsukawa et al., 2006).

Last updated June 2023 by Ankita Abnave

References:

Maizel A, Busch MA, Tanahashi T, Perkovic J, Kato M, Hasebe M, Weigel D. The floral regulator LEAFY evolves by substitutions in the DNA binding domain. Science. 2005 Apr 8;308(5719):260-3. doi: 10.1126/science.1108229. PMID: 15821093.

Anthony RG, James PE, Jordan BR. Cloning and sequence analysis of a flo/lfy homologue isolated from cauliflower (Brassica oleracea L. var. botrytis). Plant Mol Biol. 1993 Sep;22(6):1163-6. doi: 10.1007/BF00028986. PMID: 8104529.

Weigel D, Nilsson O. A developmental switch sufficient for flower initiation in diverse plants. Nature. 1995 Oct 12;377(6549):495-500. doi: 10.1038/377495a0. PMID: 7566146.

Weigel D, Alvarez J, Smyth DR, Yanofsky MF, Meyerowitz EM. LEAFY controls floral meristem identity in Arabidopsis. Cell. 1992 May 29;69(5):843-59. doi: 10.1016/0092-8674(92)90295-n. PMID: 1350515.

Zaret KS, Carroll JS. Pioneer transcription factors: establishing competence for gene expression. Genes Dev. 2011 Nov 1;25(21):2227-41. doi: 10.1101/gad.176826.111. PMID: 22056668; PMCID: PMC3219227.

Jin R, Klasfeld S, Zhu Y, Fernandez Garcia M, Xiao J, Han SK, Konkol A, Wagner D. LEAFY is a pioneer transcription factor and licenses cell reprogramming to floral fate. Nat Commun. 2021 Jan 27;12(1):626. doi: 10.1038/s41467-020-20883-w. PMID: 33504790; PMCID: PMC7840934.

Gallois JL, Nora FR, Mizukami Y, Sablowski R. WUSCHEL induces shoot stem cell activity and developmental plasticity in the root meristem. Genes Dev. 2004 Feb 15;18(4):375-80. doi: 10.1101/gad.291204. PMID: 15004006; PMCID: PMC359391.

Zhu Y, Klasfeld S, Jeong CW, Jin R, Goto K, Yamaguchi N, Wagner D. TERMINAL FLOWER 1-FD complex target genes and competition with FLOWERING LOCUS T. Nat Commun. 2020 Oct 12;11(1):5118. doi: 10.1038/s41467-020-18782-1. PMID: 33046692; PMCID: PMC7550357.

Hamès C, Ptchelkine D, Grimm C, Thevenon E, Moyroud E, Gérard F, Martiel JL, Benlloch R, Parcy F, Müller CW. Structural basis for LEAFY floral switch function and similarity with helix-turn-helix proteins. EMBO J. 2008 Oct 8;27(19):2628-37. doi: 10.1038/emboj.2008.184. Epub 2008 Sep 11. PMID: 18784751; PMCID: PMC2567413.

Coen ES, Romero JM, Doyle S, Elliott R, Murphy G, Carpenter R. floricaula: a homeotic gene required for flower development in antirrhinum majus. Cell. 1990 Dec 21;63(6):1311-22. doi: 10.1016/0092-8674(90)90426-f. PMID: 1702033.

Kyozuka J, Konishi S, Nemoto K, Izawa T, Shimamoto K. Down-regulation of RFL, the FLO/LFY homolog of rice, accompanied with panicle branch initiation. Proc Natl Acad Sci U S A. 1998 Mar 3;95(5):1979-82. doi: 10.1073/pnas.95.5.1979. PMID: 9482818; PMCID: PMC33826.

Rao NN, Prasad K, Kumar PR, Vijayraghavan U. Distinct regulatory role for RFL, the rice LFY homolog, in determining flowering time and plant architecture. Proc Natl Acad Sci U S A. 2008 Mar 4;105(9):3646-51. doi: 10.1073/pnas.0709059105. Epub 2008 Feb 27. PMID: 18305171; PMCID: PMC2265177.

Bomblies K, Wang RL, Ambrose BA, Schmidt RJ, Meeley RB, Doebley J. Duplicate FLORICAULA/LEAFY homologs zfl1 and zfl2 control inflorescence architecture and flower patterning in maize. Development. 2003 Jun;130(11):2385-95. doi: 10.1242/dev.00457. PMID: 12702653.

Tanahashi T, Sumikawa N, Kato M, Hasebe M. Diversification of gene function: homologs of the floral regulator FLO/LFY control the first zygotic cell division in the moss Physcomitrella patens. Development. 2005 Apr;132(7):1727-36. doi: 10.1242/dev.01709. Epub 2005 Mar 2. PMID: 15743879.

 N, Takagishi A, Ikari C, Takumi S, Murai K. WFL, a wheat FLORICAULA/LEAFY ortholog, is associated with spikelet formation as lateral branch of the inflorescence meristem. Genes Genet Syst. 2006 Feb;81(1):13-20. doi: 10.1266/ggs.81.13. PMID: 16607037.