Abundance of metalloprotease FtsH12 modulates chloroplast development in Arabidopsis thaliana.

The ATP-dependent metalloprotease FtsH12 (filamentation temperature sensitive protein H 12) has been suggested to participate in a heteromeric motor complex, driving protein translocation into the chloroplast. FtsH12 was immuno-detected in proplastids, seedlings, leaves, and roots. Expression of Myc-tagged FtsH12 under its native promotor allowed identification of FtsHi1, 2, 4, and 5, and plastidic NAD-malate dehydrogenase, five of the six interaction partners in the suggested import motor complex.

Reduced expression of the proteolytically inactive FtsH members has impacts on the Darwinian fitness of Arabidopsis thaliana.

FtsH (filamentation-temperature-sensitive protein H) proteases are a family of membrane-bound enzymes present in eubacteria, animals, and plants. Besides the 12 genes encoding proteolytically active members of the FtsH family in the genome of Arabidopsis, there are five genes coding for members that are assumed to be proteolytically inactive due to mutations in the protease domain; these are termed FtsHi (i for inactive). Despite their lack of proteolytic activity, these FtsHi members seem to be important for chloroplast and plant development as four out of five homozygous knockout-mutants of FtsHis are embryo-lethal.

The HhoA protease from Synechocystis sp. PCC 6803 - Novel insights into structure and activity regulation.

Proteases play a vital role in the removal of proteins, which become damaged due to temperature or oxidative stress. Important to this process in the cyanobacterium Synechocystis sp. PCC6803 is the family of Deg/HtrA proteases; HhoA (sll1679), HhoB (sll1427) and HtrA (slr1204).

Deletion of FtsH11 protease has impact on chloroplast structure and function in Arabidopsis thaliana when grown under continuous light.

The membrane-integrated metalloprotease FtsH11 of Arabidopsis thaliana is proposed to be dual-targeted to mitochondria and chloroplasts. A bleached phenotype was observed in ftsh11 grown at long days or continuous light, pointing to disturbances in the chloroplast. Within the chloroplast, FtsH11 was found to be located exclusively in the envelope.

Insights into the Cyanobacterial Deg/HtrA Proteases.

Proteins are the main machinery for all living processes in a cell; they provide structural elements, regulate biochemical reactions as enzymes, and are the interface to the outside as receptors and transporters. Like any other machinery proteins have to be assembled correctly and need maintenance after damage, e.g.

FtsH proteases located in the plant chloroplast.

FtsHs are a well-characterized family of membrane bound proteases containing an AAA (ATPase associated with various cellular activities) and a Zn(2+) metalloprotease domain. FtsH proteases are found in eubacteria, animals and plants and are known to have a crucial role in housekeeping proteolysis of membrane proteins. In Arabidopsis thaliana, 12 FtsH family members are present (FtsH 1-12) and their subcellular localization is restricted to mitochondria and chloroplasts.

Fitness analyses of Arabidopsis thaliana mutants depleted of FtsH metalloproteases and characterization of three FtsH6 deletion mutants exposed to high light stress, senescence and chilling.

Darwinian fitness analyses were performed, comparing single ftsh mutants with wild-type Arabidopsis thaliana plants grown under controlled laboratory conditions and in the field, by measuring plant size, survival rate, and silique and seed production. Additionally, three genotypes of ΔFtsH6 were analysed, under controlled growth conditions, with respect to both their ability to degrade the light-harvesting complex of photosystem II during senescence and light acclimation. In the field, substantial increases in variegation and reductions in growth were observed in the ΔFtsH2, ΔFtsH5 and ΔFtsH10 mutants; FtsH2 seemed particularly important for plant survival.

The role of phosphorylation in redox regulation of photosynthesis genes psaA and psbA during photosynthetic acclimation of mustard.

The long-term response (LTR) to light-quality gradients improves performance and survival of plants in dense stands. It involves redox-controlled transcriptional regulation of the plastome-encoded genes psaAB (encoding the P700 apoproteins of photosystem I) and psbA (encoding the D1 protein of photosystem II) and requires the action of plastid-localized kinases. To study the potential impact of phosphorylation events on plastid gene expression during the LTR, we analyzed mustard seedlings acclimated to light sources favoring either photosystem I or photosystem II.

Arabidopsis STN7 kinase provides a link between short- and long-term photosynthetic acclimation.

Flowering plants control energy allocation to their photosystems in response to light quality changes. This includes the phosphorylation and migration of light-harvesting complex II (LHCII) proteins (state transitions or short-term response) as well as long-term alterations in thylakoid composition (long-term response or LTR). Both responses require the thylakoid protein kinase STN7.

The long-term response to fluctuating light quality is an important and distinct light acclimation mechanism that supports survival of Arabidopsis thaliana under low light conditions.

The long-term response (LTR) of higher plants to varying light qualities increases the photosynthetic yield; however, the benefit of this improvement for physiology and survival of plants is largely unknown, and its functional relation to other light acclimation responses has never been investigated. To unravel positive effects of the LTR we acclimated Arabidopsis thaliana for several days to light sources, which preferentially excite photosystem I (PSI) or photosystem II (PSII). After acclimation, plants revealed characteristic differences in chlorophyll fluorescence, thylakoid membrane stacking, phosphorylation state of PSII subunits and photosynthetic yield of PSII and PSI.

Eukaryotic transcription factors in plastids--Bioinformatic assessment and implications for the evolution of gene expression machineries in plants.

The expression of genes in higher plant chloroplasts includes a complex transcriptional regulation which can be explained only in part with the action of the actually known components of the transcriptional machinery. This suggests the existence of still unknown important regulatory factors which influence chloroplast transcription. In order to test if such factors could exist we performed in silico analyses of Arabidopsis genes encoding putative transcription factors looking for putative N-terminal chloroplast transit peptides in the amino acid sequences.

Photosystem II core phosphorylation and photosynthetic acclimation require two different protein kinases.

Illumination changes elicit modifications of thylakoid proteins and reorganization of the photosynthetic machinery. This involves, in the short term, phosphorylation of photosystem II (PSII) and light-harvesting (LHCII) proteins. PSII phosphorylation is thought to be relevant for PSII turnover, whereas LHCII phosphorylation is associated with the relocation of LHCII and the redistribution of excitation energy (state transitions) between photosystems.

Photosynthetic redox control of nuclear gene expression.

Chloroplasts contain 3000-4000 different proteins but only a small subset of them is encoded in the plastid genome while the majority is encoded in the nucleus. Expression of these genes therefore requires a high degree of co-ordination between nucleus and chloroplast. This is achieved by a bilateral information exchange between both compartments including nucleus-to-plastid (anterograde) and plastid-to-nucleus (retrograde) signals.

Retrograde plastid redox signals in the expression of nuclear genes for chloroplast proteins of Arabidopsis thaliana.

Excitation imbalances between photosystem I and II generate redox signals in the thylakoid membrane of higher plants which induce acclimatory changes in the structure of the photosynthetic apparatus. They affect the accumulation of reaction center and light-harvesting proteins as well as chlorophylls a and b. In Arabidopsis thaliana the re-adjustment of photosystem stoichiometry is mainly mediated by changes in the number of photosystem I complexes, which are accompanied by corresponding changes in transcripts for plastid reaction center genes.