title: Molecular characterization of Helja, an extracellular jacalin-related protein from Helianthus annuus: Insights into the relationship of this protein with unconventionally secreted lectins.
abstract: Jacalin-related lectins (JRLs) encompass cytosolic, nuclear and vacuolar members displaying the jacalin domain in one or more copies or in combination with unrelated domains. Helianthus annuus jacalin (Helja) is a mannose-specific JRL previously identified in the apoplast of Helianthus annuus seedlings, and this protein has been proposed to follow unconventional secretion. Here, we describe the full-length Helja cDNA sequence, which presents a unique jacalin domain (merolectin) and the absence of a signal peptide, confirming that the protein cannot follow the classical ER-dependent secretory pathway. Helja mRNA is present in seeds, cotyledons, roots and hypocotyls, but no transcripts were detected in the leaves. Searches for sequence similarity showed that Helja is barely similar to other JRLs present in H. annuus databases and less than 45% identical to other monocot or dicot JRLs. Strikingly, most of the merolectins recovered through data mining using Helja as a query were predicted as apoplastic, although most of these proteins lack the signal peptide required for classical secretion. Thus, Helja is the first bait identified to recover putative unconventionally secreted lectins. Because the recovered JRLs are widely distributed among the plant kingdom, an as yet unknown role for jacalin lectins in the apoplast is emerging.
authors.affiliation: Instituto de Investigaciones Biológicas, Universidad Nacional de Mar del Plata-CONICET, Funes 3250, 7600 Mar del Plata, Argentina. Electronic address: mpinedo@mdp.edu.ar.
authors.forename: Marcela
authors.initials: M
authors.lastname: Pinedo
authors.affiliation: Instituto de Investigaciones Biológicas, Universidad Nacional de Mar del Plata-CONICET, Funes 3250, 7600 Mar del Plata, Argentina. Electronic address: facundoorts@gmail.com.
authors.forename: Facundo
authors.initials: F
authors.lastname: Orts
authors.affiliation: Laboratório de Fisiologia e Bioquímica de Microrganismos, Centro de Biociências e Biotecnologia, Universidade Estadual do Norte Fluminense, Campos dos Goytacazes 28013-602, RJ, Brazil. Electronic address: andre@uenf.br.
authors.forename: André de Oliveira
authors.initials: Ade O
authors.lastname: Carvalho
authors.affiliation: Instituto de Investigaciones Biológicas, Universidad Nacional de Mar del Plata-CONICET, Funes 3250, 7600 Mar del Plata, Argentina. Electronic address: mregente@mdp.edu.ar.
authors.forename: Mariana
authors.initials: M
authors.lastname: Regente
authors.affiliation: Instituto de Investigaciones Biológicas, Universidad Nacional de Mar del Plata-CONICET, Funes 3250, 7600 Mar del Plata, Argentina. Electronic address: julliah@hotmail.com.
authors.forename: Julia Ribeiro
authors.initials: JR
authors.lastname: Soares
authors.affiliation: Laboratório de Fisiologia e Bioquímica de Microrganismos, Centro de Biociências e Biotecnologia, Universidade Estadual do Norte Fluminense, Campos dos Goytacazes 28013-602, RJ, Brazil. Electronic address: valmg@uenf.br.
authors.forename: Valdirene Moreira
authors.initials: VM
authors.lastname: Gomes
authors.affiliation: Instituto de Investigaciones Biológicas, Universidad Nacional de Mar del Plata-CONICET, Funes 3250, 7600 Mar del Plata, Argentina. Electronic address: ldelacan@mdp.edu.ar.
authors.forename: Laura
authors.initials: L
authors.lastname: de la Canal
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D006368:Helianthus / Q000235:genetics* / Q000378:metabolism; D008969:Molecular Sequence Data; D016366:Open Reading Frames; D010802:Phylogeny; D037121:Plant Lectins / Q000737:chemistry; D010940:Plant Proteins / Q000235:genetics* / Q000378:metabolism
chemical_list: D037121:Plant Lectins; D010940:Plant Proteins; C043696:jacalin
keywords: Apoplast; Extracellular proteins; Jacalin domain; Lectin; Unconventional secretion