Secondary dormancy is an adaptive trait arising in previously non-dormant seeds due to unfavourable environmental conditions during germination. The SEED MATURATION PROTEIN1 (SMP1; AT3G12960) is involved in seed maturation and dormancy maintenance after high temperature fluctuation [
].
Small hydrophilic plant seed protein, conserved site
Type:
Conserved_site
Description:
This entry represents a conserved site in hydrophilic plant seed proteins that are structurally related:Arabidopsis thaliana proteins GEA1 and GEA6Cotton late embryogenesis abundant (LEA) protein D-19Carrot EMB-1 proteinBarley LEA proteins B19.1A, B19.1B, B19.3 and B19.4Maize late embryogenesis abundant protein Emb564Radish late seed maturation protein p8B6Rice embryonic abundant protein Emp1Sunflower 10 Kd late embryogenesis abundant protein (DS10)Wheat Em proteinsThese proteins may play a role in equipping the seed for survival, maintaining a minimal level of hydration in the dry organism and preventing the denaturation of cytoplasmic components [
,
]. They may also play a role during imbibition by controlling water uptake.
SUA is an RNA-binding protein located in the nucleus and expressed in all plant tissues. It functions as a splicing factor that influences seed maturation by controlling alternative splicing of ABI3. The suppression of the cryptic ABI3 intron indicates a role of SUA in mRNA processing. SUA also interacts with the prespliceosomal component U2AF65, the larger subunit of the conserved pre-mRNA splicing factor U2AF. SUA contains two RNA recognition motifs surrounding a zinc finger domain, an OCtamer REpeat (OCRE) domain, and a Gly-rich domain close to the C terminus [
].The OCRE (OCtamer REpeat) domain contains five repeats of an 8-residue motif, which were shown to form β-strands. Based on the architectures of proteins containing OCRE domains, a role in RNA metabolism and/or signalling has been proposed [
].
Ginkbilobin-2 (Gnk2) is an antifungal protein found in the endosperm of Ginkgo
seeds, which inhibits the growth of phytopathogenic fungi such as Fusariumoxysporum. Gnk2 has considerable homology (~85%) to embryo-abundant proteins
(EAP) from the gymnosperms Picea abies and P. glauca. Plant EAP are expressedin the late stage of seed maturation and are involved in protection against
environmental stresses such as drought. The sequence of Gnk2 is also 28-31%identical to the extracellular domain of cysteine-rich receptor-like kinases
(CRK) from the angiosperm Arabidopsis. The CRK members are induced by pathogeninfection and treatment with reactive oxygen species or salicylic acid and are
involved in the hypersensitive reaction, which is a typical system ofprogrammed cell death. In addition, there are at least 60 genes in Arabidopsis
encoding the cysteine-rich secreted proteins (CRSP) with an Gnk2-homologousdomain. Therefore, the proteins with a Gnk2-homologous domain are regarded as
one of the largest protein superfamilies, although the role of the conservedGnk2-homologous domain remains unclear [
,
].The Gnk2-homologous domain is composed of two α-helices and a fivestranded β-sheet, which forms a compact single-domain architecture with an
alpha+β-fold. It contains a C-X(8)-C-X(2)-C motif.Cysteine residues form three intramolecular disulphide bridges: C1-C5, C2-C3,
and C4-C6 [].
Ginkbilobin-2 (Gnk2) is an antifungal protein found in the endosperm of Ginkgo
seeds, which inhibits the growth of phytopathogenic fungi such as Fusariumoxysporum. Gnk2 has considerable homology (~85%) to embryo-abundant proteins
(EAP) from the gymnosperms Picea abies and P. glauca. Plant EAP are expressed
in the late stage of seed maturation and are involved in protection againstenvironmental stresses such as drought. The sequence of Gnk2 is also 28-31%
identical to the extracellular domain of cysteine-rich receptor-like kinases(CRK) from the angiosperm Arabidopsis. The CRK members are induced by pathogen
infection and treatment with reactive oxygen species or salicylic acid and areinvolved in the hypersensitive reaction, which is a typical system of
programmed cell death. In addition, there are at least 60 genes in Arabidopsisencoding the cysteine-rich secreted proteins (CRSP) with an Gnk2-homologous
domain. Therefore, the proteins with a Gnk2-homologous domain are regarded asone of the largest protein superfamilies, although the role of the conserved
Gnk2-homologous domain remains unclear [,
].The Gnk2-homologous domain is composed of two α-helices and a five
stranded β-sheet, which forms a compact single-domain architecture with analpha+β-fold. It contains a C-X(8)-C-X(2)-C motif.
Cysteine residues form three intramolecular disulphide bridges: C1-C5, C2-C3,and C4-C6 [
].
This entry represents a group of plant basic leucine zipper proteins (bZIPs), including AtbZIP8 and AtbZIP43. AtbZIP43 may act as positive regulator of BHLH109, which is associated with somatic embryogenesis (SE) induction [
].The basic (region) leucine zippers (bZIPs) are evolutionarily conserved transcription factors in eukaryotic organisms. In plants bZIPs regulate processes including pathogen defence, light and stress signalling, seed maturation and flower development [
]. The bZIP domain consists of a basic DNA-binding region and the adjacent ZIP domain. The ZIP domain consists of heptad repeats of leucine (L) or related hydrophobic amino acids. The DNA-binding region is a basic region of ~16 amino acid residues containing a nuclear localization signal followed by an invariant N-x7-R/K motif that contacts the DNA The heptad repeat of leucines or other bulky hydrophobic amino acids positioned exactly nine amino acids towards the C terminus, creating an amphipathic helix. To bind DNA, two subunits adhere via interactions between the hydrophobic sides of their helices, which creates a superimposing coiled-coil structure. The ability to form homo- and heterodimers is influenced by the electrostatic attraction and repulsion of polar residues flanking the hydrophobic interaction surface of the helices [
]. As bZIPs generally perform as dimers, heterodimerisation results in an enormous regulatory flexibility [].
This entry represents a group of plant seed storage proteins, including Napin, 2S seed storage protein and Conglutin.Napins are low-molecular weight, basic storage proteins synthesised in rape-seed embryos during seed
maturation [,
]. Sequence comparisons have revealed that Napin belongs to a diverseprotein family, which includes major allergens, trypsin inhibitors and natural anti-fungal proteins. Napin
comprises 2 polypeptide chains (MW 9000 and 4000) held together by disulphide bonds. The protein isinitially synthesised as a precursor of 178 residues, which is proteolytically cleaved to generate mature
Napin chains, with 86 and 29 residues respectively [].Some of the proteins in this family are allergens, with cores that are very resistant to proteolytic digestion and to elevated temperatures of up to 100 degrees C [
,
,
,
]. Allergies are hypersensitivity reactions of the immune system to specific substances called allergens (such as pollen, stings, drugs, or food) that, in most people, result in no symptoms. A nomenclature system has been established for antigens (allergens) that cause IgE-mediated atopic allergies in humans [WHO/IUIS Allergen Nomenclature SubcommitteeKing T.P., Hoffmann D., Loewenstein H., Marsh D.G., Platts-Mills T.A.E.,
Thomas W. Bull. World Health Organ. 72:797-806(1994)]. This nomenclature system is defined by a designation that is composed of
the first three letters of the genus; a space; the first letter of thespecies name; a space and an arabic number. In the event that two species
names have identical designations, they are discriminated from one anotherby adding one or more letters (as necessary) to each species designation.
