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Plant lipid transfer proteins: Evolution, expression and function
Linköping University, Department of Physics, Chemistry and Biology, Biology. Linköping University, The Institute of Technology.
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The plant non-specific lipid transfer proteins (nsLTPs) are known for the ability to transfer different lipids in vitro, but their in vivo functions have not yet been elucidated. They seem to play a role in the defense against biotic and abiotic stresses; the gene expression of nsLTPs is often upregulated when exposed to stresses. Further, two different nsLTPs have been shown to affect the lipid composition of the plant cuticle, a structure acting as a protective barrier. However, more evidence is needed to prove this hypothesis and to pinpoint their exact role in this process.

In this thesis I have shown that the nsLTPs are found in all land plants, but not in any of the studied algae. This supports a role in defense response, since protection against dehydration, radiation, pathogens and other stresses played a crucial role when plants adapted to a life on land. Characterization of the nsLTPs in early diverging land plant revealed that even though the amino acid similarity towards nsLTPs in flowering plants is not very high, the main properties of the proteins are still the same (Paper I). This includes the protein structure, which consists of α-helices surrounding a lipid binding cavity, a conserved pattern of cysteine residues involved in disulphide bonds and a signal sequence directing the protein to the  extracellular space. Further, the expression of nsLTPs in the moss Physcomitrella patens was shown to respond to stresses, and construction of an YFP-LTP fusion protein confirmed the localization to the periphery of the cell in planta (Paper II). Heterologous expressed Physcomitrella nsLTPs were also shown to have the ability to bind lipids and to be very heat stable, features previously only studied in nsLTPs from flowering plants. By examining the presence of a cuticle in Physcomitrella, a correlation between the nsLTPs´ lipid binding ability and the lipid composition of the cuticle could be found, which further strengthens the involvement of nsLTPs in transfer of lipids for cuticle construction.

In the flowering plant Arabidopsis thaliana, I showed that several of the nsLTPs followed the same expression pattern when examining data from different tissues, stress treatments, hormones, chemical treatments and developmental stages, but also that four of the genes were undergoing alternative splicing resulting in different isoforms of the proteins (Paper III). Based on their expression patterns, the genes could be divided into three different coexpression networks. By examining other genes similarly expressed, each network could be designated to a putative function: Transfer of lipids for synthesis of the cuticle, suberin layer and sporopollenin, respectively. In Paper IV, these hypotheses were tested in vivo by examining knockout mutants of several nsLTPs in Arabidopsis. The involvement in sporopollenin deposition could be confirmed; two of the knockout lines showed collapsed pollen grains. Further, two other lines showed an increased seed coat permeability due to an altered lipid composition of the suberin layer. Together, the results support a role for nsLTPs in construction of the protecting barriers in all land plants.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2013. , 56 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1525
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:liu:diva-98117DOI: 10.3384/diss.diva-98117ISBN: 978-91-7519-578-0 (print)OAI: oai:DiVA.org:liu-98117DiVA: diva2:652190
Public defence
2013-10-22, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:00 (English)
Opponent
Supervisors
Available from: 2013-09-30 Created: 2013-09-30 Last updated: 2013-09-30Bibliographically approved
List of papers
1. Evolutionary History of the Non-Specific Lipid Transfer Proteins
Open this publication in new window or tab >>Evolutionary History of the Non-Specific Lipid Transfer Proteins
2011 (English)In: MOLECULAR PLANT, ISSN 1674-2052, Vol. 4, no 6, 947-964 p.Article in journal (Refereed) Published
Abstract [en]

The non-specific lipid transfer proteins (nsLTPs) are small, basic proteins characterized by a tunnel-like hydrophobic cavity, capable of transferring various lipid molecules between lipid bilayers. Most nsLTPs are synthesized with an N-terminal signal peptide that localizes the protein to the apoplastic space. The nsLTPs have only been identified in seed plants, where they are encoded by large gene families. We have initiated an analysis of the evolutionary history of the nsLTP family using genomic and EST information from non-seed land plants and green algae to determine: (1) when the nsLTP family arose, (2) how often new nsLTP subfamilies have been created, and (3) how subfamilies differ in their patterns of expansion and loss in different plant lineages. In this study, we searched sequence databases and found that genes and transcripts encoding nsLTPs are abundant in liverworts, mosses, and all other investigated land plants, but not present in any algae. The tertiary structures of representative liverwort and moss nsLTPs were further studied with homology modeling. The results indicate that the nsLTP family has evolved after plants conquered land. Only two of the four major subfamilies of nsLTPs found in flowering plants are present in mosses and liverworts. The additional subfamilies have arisen later, during land plant evolution. In this report, we also introduce a modified nsLTP classification system.

Place, publisher, year, edition, pages
Oxford University Press (OUP): Policy B / Oxford University Press (OUP), 2011
Keyword
Lipids; evolutionary genetics; molecular biology; molecular evolution; bryophytes; ferns
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-73738 (URN)10.1093/mp/ssr019 (DOI)000297377100003 ()
Available from: 2012-01-12 Created: 2012-01-12 Last updated: 2013-09-30
2. Characterization of GPI-anchored lipid transfer proteins in Physcomitrella patens
Open this publication in new window or tab >>Characterization of GPI-anchored lipid transfer proteins in Physcomitrella patens
Show others...
2014 (English)In: Plant physiology and biochemistry (Paris), ISSN 0981-9428, E-ISSN 1873-2690, Vol. 75, 55-69 p.Article in journal (Refereed) Published
Abstract [en]

The non-specific lipid transfer proteins (nsLTPs) are characterized by a compact structure with a central hydrophobic cavity very suitable for binding hydrophobic ligands, such as lipids. The nsLTPs are encoded by large gene families in all land plant lineages, but seem to be absent from green algae. The nsLTPs are classified to different types based on molecular weight, sequence similarity, intron position or spacing between the cysteine residues. The Type G nsLTPs (LTPGs) have a GPI-anchor in the C-terminal region which may attach the protein to the exterior side of the plasma membrane. Here, we present the first characterization of nsLTPs from an early diverged plant, the moss Physcomitrella patens. Physcomitrella LTPGs were heterologously produced and purified from Pichia pastoris. The purified moss LTPGs were found to be extremely heat stable and showed a binding preference for unsaturated fatty acids. Expression of a moss LTPG-YFP fusion revealed localization to the plasma membrane. The expression of many of the moss LTPGs were found to be upregulated during drought and cold treatments. Lipid profiling revealed that cutin monomers, such as C16 and C18 mono- and di-hydroxylated fatty acids, could be identified in Physcomitrella.

Place, publisher, year, edition, pages
Elsevier, 2014
Keyword
LTP; lipid transfer protein; cutin; moss; Physcomitrella patens
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-98112 (URN)10.1016/j.plaphy.2013.12.001 (DOI)000331496000007 ()
Available from: 2013-09-30 Created: 2013-09-30 Last updated: 2017-12-06
3. Coexpression patterns indicate that GPI-anchored non-specific lipid transfer proteins are involved in accumulation of cuticular wax, suberin and sporopollenin
Open this publication in new window or tab >>Coexpression patterns indicate that GPI-anchored non-specific lipid transfer proteins are involved in accumulation of cuticular wax, suberin and sporopollenin
Show others...
2013 (English)In: Plant Molecular Biology, ISSN 0167-4412, E-ISSN 1573-5028, Vol. 83, no 6, 625-649 p.Article in journal (Refereed) Published
Abstract [en]

The non-specific lipid transfer proteins (nsLTP) are unique to land plants. The nsLTPs are characterized by a compact structure with a central hydrophobic cavity and can be classified to different types based on sequence similarity, intron position or spacing between the cysteine residues. The type G nsLTPs (LTPGs) have a GPI-anchor in the C-terminal region which attaches the protein to the exterior side of the plasma membrane. The function of these proteins, which are encoded by large gene families, has not been systematically investigated so far. In this study we have explored microarray data to investigate the expression pattern of the LTPGs in Arabidopsis and rice. We identified that the LTPG genes in each plant can be arranged in three expression modules with significant coexpression within the modules. According to expression patterns and module sizes, the Arabidopsis module AtI is functionally equivalent to the rice module OsI, AtII corresponds to OsII and AtIII is functionally comparable to OsIII. Starting from modules AtI, AtII and AtIII we generated extended networks with Arabidopsis genes coexpressed with the modules. Gene ontology analyses of the obtained networks suggest roles for LTPGs in the synthesis or deposition of cuticular waxes, suberin and sporopollenin. The AtI-module is primarily involved with cuticular wax, the AtII-module with suberin and the AtIII-module with sporopollenin. Further transcript analysis revealed that several transcript forms exist for several of the LTPG genes in both Arabidopsis and rice. The data suggests that the GPI-anchor attachment and localization of LTPGs may be controlled to some extent by alternative splicing.

Place, publisher, year, edition, pages
Springer Netherlands, 2013
Keyword
LTP, Lipid transfer protein, Wax, Sporopollenin, Suberin, Coexpression, Microarray, Alternative splicing
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-98111 (URN)10.1007/s11103-013-0113-5 (DOI)000327093600008 ()23893219 (PubMedID)
Available from: 2013-09-30 Created: 2013-09-30 Last updated: 2017-12-06Bibliographically approved
4. GPI-anchored lipid transfer proteins are involved in the development of seed coats and pollen in Arabidopsis
Open this publication in new window or tab >>GPI-anchored lipid transfer proteins are involved in the development of seed coats and pollen in Arabidopsis
(English)Manuscript (preprint) (Other academic)
Abstract [en]

The non-specific lipid transfer proteins (nsLTPs) constitute a large protein family specific for plants. Proteins from the family are found in all land plants, but have not been identified in green algae. Their in vivo functions are still disputed although evidence is accumulating for a role of these proteins in cuticle development. In a previous study we performed a coexpression analysis of GPI-anchored nsLTPs (LTPGs) that suggested that these proteins also are involved in the accumulation of suberin and sporopollenin. Here, we follow up the previous co-expression study by characterising the phenotypes of Arabidopsis lines with insertions in LTPG genes. The observed phenotypes include an inability to limit tetrazolium salt uptake in seeds, development of hair-like structures on seeds, altered pollen morphologies and decreased levels of ω-hydroxy fatty acids in seed coats. The observed phenotypes give further support for a role in suberin and sporopollenin biosynthesis or deposition in Arabidopsis.

Keyword
LTP; lipid transfer protein; seed coat; pollen; sporopollenin; suberin; fatty acids
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-98114 (URN)
Available from: 2013-09-30 Created: 2013-09-30 Last updated: 2013-09-30Bibliographically approved

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