The molecular basis of high light photoacclimation in diatoms
The photosynthetic efficiency and productivity of diatoms may depend on the light environment which can be highly variable in aquatic ecosystems. To maintain opitmal photosynthesis in a permanently changing environment, diatoms have evolved a number of regulatory mechnanisms. The photoprotective NPQ (non-photochemical fluorescence quenching) process allows the plastid to safely dissipate the excess energy absorbed during a light stress. The extend of NPQ can be rather high in diatoms. Xanthophyll pigmentns and specific light-harvesting complex (LHC) polypeptides are necessary for the NPQ mechanism. We want to address the question how the organization and composition (polypeptide and pigment) of the LHC antenna enable the diatoms to cope with the stressful iincrease of light intensity. Especially, we want to gain knowledge on the LHC polypeptide(s) involved in the response of the cells to hight light, and to identify the special LHC antenna polypeptide(s) possibly involved iin the control of the NPQ process. In this context, we will focus on a particular group of these polypeptids: the High Light Induced Proteins (HLIPs). In diatoms, nothing is known concerning their location in the LHC antenna, their regulation as a function of light at the gene and protein levels, and their role in the physiological response of the diatoms to high light stress. We will study these aspects of the acclimation to high light in diatoms by coupling a proteomic approach on the LHC system, gene expression analysis versus light, <it>in vivo</it> genetic modulation of HLIPs and physiological characterisation.
- Lavaud, Johann - Project head
- FB Biologie
|(2012): Silencing of the violaxanthin de-epoxidase gene in the diatom Phaeodactylum tricornutum reduces diatoxanthin synthesis and non-photochemical quenching PLoS ONE ; 7 (2012), 5. - e36806. - eISSN 1932-6203||
Silencing of the violaxanthin de-epoxidase gene in the diatom Phaeodactylum tricornutum reduces diatoxanthin synthesis and non-photochemical quenching
Diatoms are a major group of primary producers ubiquitous in all aquatic ecosystems. To protect themselves from photooxidative damage in a fluctuating light climate potentially punctuated with regular excess light exposures, diatoms have developed several photoprotective mechanisms. The xanthophyll cycle (XC) dependent non-photochemical chlorophyll fluorescence quenching (NPQ) is one of the most important photoprotective processes that rapidly regulate photosynthesis in diatoms. NPQ depends on the conversion of diadinoxanthin (DD) into diatoxanthin (DT) by the violaxanthin de-epoxidase (VDE), also called DD de-epoxidase (DDE). To study the role of DDE in controlling NPQ, we generated transformants of P. tricornutum in which the gene (Vde/Dde) encoding for DDE was silenced. RNA interference was induced by genetic transformation of the cells with plasmids containing either short (198 bp) or long (523 bp) antisense (AS) fragments or, alternatively, with a plasmid mediating the expression of a self-complementary hairpin-like construct (inverted repeat, IR). The silencing approaches generated diatom transformants with a phenotype clearly distinguishable from wildtype (WT) cells, i.e. a lower degree as well as slower kinetics of both DD de-epoxidation and NPQ induction. Real-time PCR based quantification of Dde transcripts revealed differences in transcript levels between AS transformants and WT cells but also between AS and IR transformants, suggesting the possible presence of two different gene silencing mediating mechanisms. This was confirmed by the differential effect of the light intensity on the respective silencing efficiency of both types of transformants. The characterization of the transformants strengthened some of the specific features of the XC and NPQ and confirmed the most recent mechanistic model of the DT/NPQ relationship in diatoms.
|Period:||01.10.2006 – 30.09.2009|