title: Molecular cloning and transcriptional activity of a new Petunia calreticulin gene involved in pistil transmitting tract maturation, progamic phase, and double fertilization.
abstract: Calreticulin (CRT) is a highly conserved and ubiquitously expressed Ca²⁺-binding protein in multicellular eukaryotes. As an endoplasmic reticulum-resident protein, CRT plays a key role in many cellular processes including Ca²⁺ storage and release, protein synthesis, and molecular chaperoning in both animals and plants. CRT has long been suggested to play a role in plant sexual reproduction. To begin to address this possibility, we cloned and characterized the full-length cDNA of a new CRT gene (PhCRT) from Petunia. The deduced amino acid sequence of PhCRT shares homology with other known plant CRTs, and phylogenetic analysis indicates that the PhCRT cDNA clone belongs to the CRT1/CRT2 subclass. Northern blot analysis and fluorescent in situ hybridization were used to assess PhCRT gene expression in different parts of the pistil before pollination, during subsequent stages of the progamic phase, and at fertilization. The highest level of PhCRT mRNA was detected in the stigma-style part of the unpollinated pistil 1 day before anthesis and during the early stage of the progamic phase, when pollen is germinated and tubes outgrow on the stigma. In the ovary, PhCRT mRNA was most abundant after pollination and reached maximum at the late stage of the progamic phase, when pollen tubes grow into the ovules and fertilization occurs. PhCRT mRNA transcripts were seen to accumulate predominantly in transmitting tract cells of maturing and receptive stigma, in germinated pollen/growing tubes, and at the micropylar region of the ovule, where the female gametophyte is located. From these results, we suggest that PhCRT gene expression is up-regulated during secretory activity of the pistil transmitting tract cells, pollen germination and outgrowth of the tubes, and then during gamete fusion and early embryogenesis.
authors.affiliation: Laboratory of Isotope and Instrumental Analysis, Faculty of Biology and Environment Protection, Nicolaus Copernicus University, Toruń, Poland, rlenart@umk.pl.
authors.forename: Robert
authors.initials: R
authors.lastname: Lenartowski
authors.forename: Anna
authors.initials: A
authors.lastname: Suwińska
authors.forename: Justyna
authors.initials: J
authors.lastname: Prusińska
authors.forename: Krzysztof
authors.initials: K
authors.lastname: Gumowski
authors.forename: Marta
authors.initials: M
authors.lastname: Lenartowska
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D002118:Calcium / Q000378:metabolism*; D002135:Calcium-Binding Proteins / Q000235:genetics / Q000378:metabolism; D037282:Calreticulin / Q000235:genetics* / Q000378:metabolism; D018076:DNA, Complementary / Q000737:chemistry / Q000235:genetics; D018744:DNA, Plant / Q000737:chemistry / Q000235:genetics; D035264:Flowers / Q000166:cytology / Q000235:genetics / Q000502:physiology; D015870:Gene Expression; D018506:Gene Expression Regulation, Plant; D006706:Homeostasis; D008969:Molecular Sequence Data; D032306:Petunia / Q000166:cytology / Q000235:genetics* / Q000502:physiology; D010802:Phylogeny; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D011058:Pollen / Q000166:cytology / Q000235:genetics / Q000502:physiology; D054817:Pollination; D017434:Protein Structure, Tertiary; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA
chemical_list: D002135:Calcium-Binding Proteins; D037282:Calreticulin; D018076:DNA, Complementary; D018744:DNA, Plant; D010940:Plant Proteins; C085577:Ca2+-binding protein-1; D002118:Calcium