title: Ice recrystallization inhibition proteins of perennial ryegrass enhance freezing tolerance.
abstract: Ice recrystallization inhibition (IRI) proteins are thought to play an important role in conferring freezing tolerance in plants. Two genes encoding IRI proteins, LpIRI-a and LpIRI-b, were isolated from a relatively cold-tolerant perennial ryegrass cv. Caddyshack. Amino acid alignments among the IRI proteins revealed the presence of conserved repetitive IRI-domain motifs (NxVxxG/NxVxG) in both proteins. Quantitative reverse transcriptase PCR (qRT-PCR) analysis indicated that LpIRI-a was up-regulated approximately 40-fold while LpIRI-b was up-regulated sevenfold after just 1 h of cold acclimation, and by 7 days of cold acclimation the transcripts had increased 8,000-fold for LpIRI-a and 1,000-fold for LpIRI-b. Overexpression of either LpIRI-a or LpIRI-b gene in Arabidopsis increased survival rates of the seedlings following a freezing test under both cold-acclimated and nonacclimated conditions. For example, without cold acclimation a -4 degrees C treatment reduced the wild type's survival rate to an average of 73%, but resulted in survival rates of 85-100% for four transgenic lines. With cold acclimation, a -12 degrees C treatment reduced the wild type's survival rate to an average of 38.7%, while it resulted in a survival rate of 51-78.5% for transgenic lines. After cold acclimation, transgenic Arabidopsis plants overexpressing either LpIRI-a or LpIRI-b gene exhibited a consistent reduction in freezing-induced ion leakage at -8, -9, and -10 degrees C. Furthermore, the induced expression of the LpIRI-a and LpIRI-b proteins in transgenic E. coli enhanced the freezing tolerance in host cells. Our results suggest that IRI proteins play an important role in freezing tolerance in plants.
authors.affiliation: Department of Horticulture, Iowa State University, Ames, IA 50011-1100, USA.
authors.forename: Chunzhen
authors.initials: C
authors.lastname: Zhang
authors.forename: Shui-zhang
authors.initials: SZ
authors.lastname: Fei
authors.forename: Rajeev
authors.initials: R
authors.lastname: Arora
authors.forename: David J
authors.initials: DJ
authors.lastname: Hannapel
mesh_terms: D000222:Adaptation, Physiological; D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000235:genetics; D001483:Base Sequence; D003460:Crystallization; D017931:DNA Primers; D005615:Freezing; D007053:Ice; D008129:Lolium / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D008969:Molecular Sequence Data; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D030821:Plants, Genetically Modified; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017386:Sequence Homology, Amino Acid
chemical_list: D017931:DNA Primers; D007053:Ice; D010940:Plant Proteins