Influence of knockout of At4g20990 gene encoding α-CA4 on photosystem II light-harvesting antenna in plants grown under different light intensities and day lengths

Abstract

Effect of knockout of the At4g20990 gene encoding α-carbonic anhydrase 4 (α-CA4) in Arabidopsis thaliana in plants grown in low light (LL, 80 μmol photons m s) or in high light (HL, 400 μmol photons m s) under long (LD, 16 h) or short (SD, 8 h) day length was studied. In α-CA4 knockout plants, under all studied conditions, the non-photochemical quenching was lower; the decrease was more pronounced under HL. This pointed to α-CA4 implication in the processes leading to energy dissipation in PSII antenna. In this context the content of major antenna proteins Lhcb1 and Lhcb2 was lower in α-CA4 knockouts than in wild-type (WT) plants under all growth conditions. The expression level of lhcb2 gene was also lower in mutants grown under LD, LL and HL in comparison to WT. At the same time, this level was higher in mutants grown under SD, LL and it was the same under SD, HL. Overall, the data showed that the knockout of the At4g20990 gene affected both the contents of proteins of PSII light-harvesting complex and the expression level of genes encoding these proteins, with peculiarities dependent on day length. These data together with the fact of a decrease of non-photochemical quenching of leaf chlorophyll a fluorescence in α-CA4-mut as compared with that in WT plants implied that α-CA4 participates in acclimation of photosynthetic apparatus to light intensity, possibly playing important role in the photoprotection. The role of this CA can be especially important in plants growing under high illumination conditions.

Role of Plant Carbonic Anhydrases under Stress Conditions

“…The exact position of β-CA5 in Arabidopsis chloroplasts is unknown, but it cannot be excluded that there are two forms of this enzyme with one located in the chloroplast envelope (see above) and the other situated in the thylakoid lumen. The expression level of the At4g33580 gene encoding β-CA5 is 2-3 orders lower than that of, for example, the At3g01500 gene encoding stromal β-CA1 in plants grown at atmospheric CO 2 concentration in low-light conditions [135]. The transcription intensity of the gene encoding β-CA5 was higher when illumination decreased both in short-day and long-day conditions.…”

“…Since the energy-dependent quenching (the part of the NPQ that is associated with the accumulation of protons in the thylakoid lumen) is the main process, which had the effect on changes in NPQ , we suggested that α-CA4 is involved in the protonation of either PsbS protein or violaxantin deepoxidase. The role of α-CA4 in NPQ in PSII antenna was confirmed by the fact that the knockout of the At4g20990 gene affected both the protein content of the light-harvesting complex PSII and the expression level of the genes encoding these proteins [135]. The content of the major PSII antenna proteins, Lhcb1, and Lhcb2 was lower in α-CA4 knockouts than in the WT plants.…”

“…The knockout of α-ca2 gene has led to the opposite changes in the properties of plants compared with those resulting from the knockout of α-ca4 gene. Fresh leaf weight, chlorophyll a/chlorophyll b ratio, and starch and H 2 O 2 content in leaves of α-CA2 mutants were lower than in the WT plants, while CO assimilation rate was higher [37,134,135]. In α-CA2 knockouts, the effective quantum yield of photosynthetic electron transport was lower than in WT, while NPQ was higher, also due to the energy-dependent component.…”

“…We have shown that the fresh weight of the plant leaves with knocked-out α-ca4 gene was 10% higher, the starch and H 2 O 2 content was significantly higher, and the rate of CO 2 assimilation in leaves was lower in comparison to WT plants. The effective quantum yield of photosynthetic electron transport at saturating light intensity and CO 2 concentration was higher in mutants than in the WT, while nonphotochemical chlorophyll fluorescence quenching (NPQ ) was lower [13,37,134,135]. The content of transcripts of the At4g20990 gene encoding α-CA4 was two times higher under high (400 μmol quanta m −2 s −1 ) than under low illumination (80 μmol quanta m −2 s −1 ) when grown under "short-day" (8 hours day/16 hours night) and 16 times higher under "long-day" conditions (16 hours day/8 hours night) [6].…”

Transport and Use of Bicarbonate in Plants: Current Knowledge and Challenges Ahead

“…αCa1 is expressed in chloroplasts and αCA2 is expressed in the plasma membrane. α-CA4 is implicated in the processes leading to energy dissipation in the PSII antenna [ 154 ]. Arabidopsis αCA8 is clearly a pseudogene since it encodes in-frame stop codons [ 147 ].…”