| 1. |
- Alexandersson, Erik, et al.
(författare)
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Whole gene family expression and drought stress regulation of aquaporins
- 2005
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Ingår i: Plant Molecular Biology. - : Springer Science and Business Media LLC. - 1573-5028 .- 0167-4412. ; 59:3, s. 469-484
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Tidskriftsartikel (refereegranskat)abstract
- Since many aquaporins (AQPs) act as water channels, they are thought to play an important role in plant water relations. It is therefore of interest to study the expression patterns of AQP isoforms in order to further elucidate their involvement in plant water transport. We have monitored the expression patterns of all 35 Arabidopsis AQPs in leaves, roots and flowers by cDNA microarrays, specially designed for AQPs, and by quantitative real-time reverse transcriptase PCR (Q-RT-PCR). This showed that many AQPs are pre-dominantly expressed in either root or flower organs, whereas no AQP isoform seem to be leaf specific. Looking at the AQP subfamilies, most plasma membrane intrinsic proteins (PIPs) and some tonoplast intrinsic proteins (TIPs) have a high level of expression, while NOD26-like proteins (NIPs) are present at a much lower level. In addition, we show that PIP transcripts are generally down-regulated upon gradual drought stress in leaves, with the exception of AtPIP1;4 and AtPIP2;5, which are up-regulated. AtPIP2;6 and AtSIP1;1 are constitutively expressed and not significantly affected by the drought stress. The transcriptional down-regulation of PIP genes upon drought stress could also be observed on the protein level.
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| 2. |
- Forsberg, Jens, et al.
(författare)
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Redox signalling in chloroplasts and mitochondria: genomic and biochemical evidence for two-component regulatory systems in bioenergetic organelles
- 2001
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Ingår i: Biochemical Society Transactions. - 0300-5127. ; 29:4, s. 403-407
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Tidskriftsartikel (refereegranskat)abstract
- Redox chemistry is central to the primary functions of chloroplasts and mitochondria, that is, to energy conversion in photosynthesis and respiration. However, these bioenergetic organelles always contain very small, specialized genetic systems, relics of their bacterial origin. At huge cost, organellar genomes contain, typically, a mere 0.1% of the genetic information in a eukaryotic cell. There is evidence that chloroplast and mitochondrial genomes encode proteins whose function and biogenesis are particularly tightly governed by electron transfer. We have identified nuclear genes for 'bacterial' histidine sensor kinases and aspartate response regulators that seem to be targeted to chloroplast and mitochondrial membranes. Sequence similarities to cyanobacterial redox signalling components indicate homology and suggest conserved sensory and signalling functions. Two-component redox signalling pathways might be ancient, conserved mechanisms that permit endogenous control over the biogenesis, in situ, of bioenergetic complexes of chloroplasts and mitochondria.
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| 3. |
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| 4. |
- Fraysse, Laure
(författare)
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Plant major intrinsic proteins - functional implications of expression and localisation studies
- 2003
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Plant water channels are members of the very old Major Intrinsic Protein (MIP) family, with representatives in bacteria, fungi, animals, and plants. The genome of the model plant Arabidopsis thaliana contains 35 MIP genes. Based on protein sequence comparisons, the MIP family has been divided in four subfamilies: the PIP (Plasma membrane Intrinsic Protein), the TIP (Tonoplast Intrinsic Protein), the NIP (NOD26-like Intrinsic Protein), and the SIP (Small basic Intrinsic Protein) subfamilies. In order to harmonise the names of MIP members in all plant species, a nomenclature has been proposed, which is now broadly accepted. The increasing number of sequences from various plant species, including non-vascular plants, angiosperms, and conifers, provides information concerning the evolution of the MIP family in plants. In particular, the highly conserved PIP subfamily is divided into two groups, PIP1 and PIP2. The relatively large number of PIPs (13 in Arabidopsis) and the high degree of conservation within this subfamily point to important roles for these proteins in plants and to the existence of a high selective pressure on genes of both the PIP1 and the PIP2 groups in evolution. The recently solved structures of a mammal aquaporin, AQP1, and a bacterial glycerol facilitator, GlpF indicate that the overall fold of all members of the MIP family is likely to be conserved. However, a comparison of the sequences of these proteins and that of plant MIPs from different subfamilies indicates that members of the different MIP subfamilies probably exhibit different substrate specificities. Interestingly, PIP1 and PIP2 proteins purified from spinach show clear structural differences, implying that members of the two different groups in the PIP subfamily have different transport properties. MIP genes have been shown to be regulated at the transcriptional level by abiotic and biotic factors. Microarrays have been designed in order to investigate the expression of all Arabidopsis MIP genes. Data from a study of the organ specificity of MIP genes are presented. Results of reverse genetics studies suggest that the major substrate of PIPs is water. Immunolabelling studies of two PIP1 isoforms in spinach, together with similar studies in other species, indicate that PIP1 homologues are involved in phloem transport and guard cell movements. Future work should address the roles of the PIP1 proteins in these cells, and possible modes of post-translational regulation in planta.
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| 5. |
- Fraysse, Laure, et al.
(författare)
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Specific plasma membrane aquaporins of the PIP1 subfamily are expressed in sieve elements and guard cells
- 2005
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Ingår i: Biology of the Cell. - 0248-4900. ; 97:7, s. 519-534
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Tidskriftsartikel (refereegranskat)abstract
- Background information. Transmembrane water flow is aided by water-specific channel proteins, aquaporins. Plant genomes code for approx. 35 expressed and functional aquaporin isoforms. Plant aquaporins fall into four different subfamilies of which the PIPS (plasma membrane intrinsic proteins) constitute the largest and evolutionarily most conserved subfamily with 13 members in Arabidopsis and maize. Furthermore, the PIPs can be divided into two phylogenetic groups, PIP1 and PIP2, of which the PIP1 isoforms are most tightly conserved, sharing > 90% amino acid sequence identity. As the nomenclature implies, the majority of PIPs have been shown to be localized at the plasma membrane. Recently, two highly abundant plasma membrane aquaporins, SoPIP2;1 and SoPIP1;2, have been purified and structurally characterized. Results. We report the cloning of a cDNA encoding SoPIP1;2 and show that there are at least five additional sequences homologous with SoPIP2;1 and SoPIP1;2 in the spinach genome. To understand their role in planta, we have investigated the cellular localization of the aquaporin homologues SoPIP1;2 and SoPIP1;1. By Western and Northern-blot analyses and by immunocytochemical detection at the light and electron microscopic levels, we show that SoPIP1;2 is highly expressed in phloem sieve elements of leaves, roots and petioles and that SoPIP1;1 is present in stomatal guard cells. Conclusions. Localization of the two abundant aquaporin isoforms suggests roles for specific PIPs of the PIP1 subgroup in phloem loading, transport and unloading, and in stomatal movements.
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| 6. |
- Johanson, Urban, et al.
(författare)
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The complete set of genes encoding major intrinsic proteins in Arabidopsis provides a framework for a new nomenclature for major intrinsic proteins in plants
- 2001
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Ingår i: Plant Physiology. - : Oxford University Press (OUP). - 1532-2548 .- 0032-0889. ; 126:4, s. 1358-1369
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Tidskriftsartikel (refereegranskat)abstract
- Major intrinsic proteins (MIPs) facilitate the passive transport of small polar molecules across membranes. MIPs constitute a very old family of proteins and different forms have been found in all kinds of living organisms, including bacteria, fungi, animals, and plants. In the genomic sequence of Arabidopsis, we have identified 35 different MIP-encoding genes. Based on sequence similarity, these 35 proteins are divided into four different subfamilies: plasma membrane intrinsic proteins, tonoplast intrinsic proteins, NOD26-like intrinsic proteins also called NOD26-like MIPs, and the recently discovered small basic intrinsic proteins. In Arabidopsis, there are 13 plasma membrane intrinsic proteins, 10 tonoplast intrinsic proteins, nine NOD26-like intrinsic proteins, and three small basic intrinsic proteins. The gene structure in general is conserved within each subfamily, although there is a tendency to lose introns. Based on phylogenetic comparisons of maize (Zea mays) and Arabidopsis MIPs (AtMIPs), it is argued that the general intron patterns in the subfamilies were formed before the split of monocotyledons and dicotyledons. Although the gene structure is unique for each subfamily, there is a common pattern in how transmembrane helices are encoded on the exons in three of the subfamilies. The nomenclature for plant MIPs varies widely between different species but also between subfamilies in the same species. Based on the phylogeny of all AtMIPs, a new and more consistent nomenclature is proposed. The complete set of AtMIPs, together with the new nomenclature, will facilitate the isolation, classification, and labeling of plant MIPs from other species.
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