Disease relevance of psaI

• The psbO gene of cyanobacteria, green algae and higher plants encodes the precursor of the 33 kDa manganese-stabilizing protein (MSP), a water-soluble subunit of photosystem II (PSII) [1].

High impact information on psaI

• Photosystem II (PSII) is a key component of photosynthesis, the process of converting sunlight into the chemical energy of life [2].
• When PSII is favoured (state 2), the redox conditions in the thylakoids change and result in activation of a protein kinase [3].
• However, there was a major change in the macroorganization of PSII within these membranes; electron microscopy and image analysis revealed the complete absence of the C(2)S(2)M(2) light-harvesting complex II (LHCII)/PSII supercomplex predominant in wild-type plants [4].
• To gain insight into the processes involved in photosystem II (PSII) biogenesis and maintenance, we characterized the low psii accumulation1 (lpa1) mutant of Arabidopsis thaliana, which generally accumulates lower than wild-type levels of the PSII complex [5].
• We identified two such mechanisms: nonphotochemical energy dissipation (NPQ) in photosystem II (PSII) and synthesis of zeaxanthin [6].

Biological context of psaI

• PsbH and PsbB are essential requirements for PSII assembly in photosynthetic eukaryotes, and their absence in hcf107 is consistent with the PSII-less mutant phenotype [7].
• Using light sources that predominantly excite either photosystem I (PSI) or photosystem II (PSII), we modulated photosynthetic electron transport in tobacco, Arabidopsis, and Lemna sprouts [8].
• This rapid process is referred to as a state transition and has been correlated with the phosphorylation and migration of the light-harvesting complex protein (LHCP) between PSII and PSI [9].
• While PSII photoinhibition was similar in wild type and lut2 npq2 exposed to high light at low temperature, the double mutant was much more resistant to photooxidative stress and lipid peroxidation than the wild type [10].
• When the wild type and lcd1-1 are exposed to short-term high-light stress, leaves do not bleach in lcd1-1 and potential activities of photosystems I (PSI) and II (PSII) decrease to a similar extent in both the genotypes, indicating that the photosynthetic apparatus is not affected by lcd1-1 mutation [11].

Anatomical context of psaI

• The low protective efficiency of NPQ supports the conclusion that the Chl antenna of PSII is not the only photoreceptor of photoinhibition [12].

Associations of psaI with chemical compounds

• We conclude that, in cooperation with the xanthophyll cycle, vitamin E fulfills at least two different functions in chloroplasts at the two major sites of singlet oxygen production: preserving PSII from photoinactivation and protecting membrane lipids from photooxidation [6].
• However, a sucrose gradient separation of briefly solubilized thylakoid membranes revealed that no dimeric PSII supracomplex could be detected in the transgenic plants lacking the PsbW protein [13].
• We propose that these effects result in an increased population of reduced primary electron-accepting quinone in PSII, facilitating non-radiative P680(+)Q(A)(-) radical pair recombination [14].
• We found that changes in phenol metabolism result in altered rates of PSII reaction center heterodimer degradation under mixtures of photosynthetically active radiation and UV-B [15].
• These results suggested that a deficiency of phylloquinone in PSI caused the abolishment of PSI and a partial defect of PSII due to a significant decrease of plastoquinone, but did not influence the ultrastructure of the chloroplasts in young leaves [16].

Analytical, diagnostic and therapeutic context of psaI

• Although the structure of PSII has been resolved by x-ray crystallography, the mechanism underlying its assembly is poorly understood [17].
• Transmission electron microscopy aided by single-particle image analysis was applied to the ordered arrays and the isolated PSII complexes [18].
• Using parallel time-resolved and pulse-amplitude modulation fluorometry, we studied the influence of the intrathylakoid pH and the xanthophyll cycle carotenoids on the PSII chlorophyll (Chl) a fluorescence yield in thylakoids of Arabidopsis, spinach, and barley [19].
• Gel blot analysis and affinity chromatography of solubilized thylakoid membranes suggest that HCF136p associates with a PSII precomplex containing at least D2 and cytochrome b(559) [20].
• Two other PSII genes, psbA (chloroplast-encoded) and psbP (nuclear-encoded), isolated by degenerate primer PCR, display a similar trend in expression [21].

References