Effect of light intensity under different photoperiods on expression level of carbonic anhydrase genes of the α- and β-families in Arabidopsis thaliana leaves

Abstract

Changes in expression levels of genes encoding carbonic anhydrases α-CA1, α-CA2, α-CA4, β-CA1, β-CA2, β-CA3, β-CA4, β-CA5, and β-CA6 in Arabidopsis thaliana leaves after light increase from 80 to 400 µmol PAR quanta·m·s were investigated under short day (8 h) and long day (16 h) photoperiods. The expression of two forms of the gene, At3g01500.2 and At3g01500.3, encoding the most abundant carbonic anhydrase of leaves, β-CA1, situated in chloroplast stroma, was found. The content of At3g01500.3 transcripts was higher by approximately an order of magnitude compared to the content of At3g01500.2 transcripts. When plants were adapted to high light intensity under short day photoperiod, the expression level of both forms increased, whereas under long day photoperiod, the content of At3g01500.3 transcripts increased, and the content of transcripts of At3g01500.2 decreased. The expression levels of the At3g01500.3 gene and of genes encoding chloroplast carbonic anhydrases α-CA1, α-CA4, α-CA2 and cytoplasmic carbonic anhydrase β-CA2 increased significantly in response to increase in light intensity under short day, and these of the first three genes increased under long day as well. The expression level of the gene encoding α-CA2 under long day photoperiod as well as of genes of chloroplast β-CA5 and β-CA4 from plasma membranes and mitochondrial β-CA6 under both photoperiods depended insignificantly on light intensity. Hypotheses about the roles in higher plant metabolism of the studied carbonic anhydrases are discussed considering the effects of light intensity on expression levels of the correspondent genes.

Role of Plant Carbonic Anhydrases under Stress Conditions

“…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]. Thus, the above-described effects of the At4g20990 gene knockout are consistent with a significant increase in the expression level of this gene in plants under high illumination; these are the conditions where the activation of NPQ , which protects PSII from photoinhibition, is important.…”

“…The data on the decrease in photosynthetic activity, as well as the ability to accumulate starch in plants with a knockout of the gene encoding α-CA1 [116], may indicate the role of α-CA1 in photosynthesis and the possibility that this CA is involved in CO 2 supply to Rubisco. Using primers designed for possible alternative splicing of the template RNA of the At3g01500 gene encoding β-CA1, two isoforms were found to be present in the leaves of Arabidopsis [6]. An increase in plant illumination led to a change in the content of transcripts of most genes encoding CA of chloroplasts, and a significant difference was observed in the expression intensity of α-CA1 genes and two forms of β-CA1.…”

“…The opposite effect of increasing the light intensity on the content of transcripts of two RNA forms of a gene encoding β-CA1, an increase in the content of transcripts of one form and a decrease in the other, can indicate different functions of the proteins encoded by them. An increase in the expression of α-CA1 and one of the forms of RNA of the β-ca1 gene with increased illumination suggests their cooperation in the CO 2 supply to Rubisco [6]. In general, it can be assumed, on the basis of the available data, that plant CAs, as a rule, jointly control one or another metabolic process.…”

“…At the same time, the story is much more complicated since C3 plants have a large number of genes encoding CAs, the physiological role of which has not been established yet. It is still not entirely clear whether all these genes are expressed, since the expression of a number of CA genes is induced under certain conditions, such as low CO 2 [5] and high illumination [6] and osmotic stress [7].…”

Carbonic Anhydrases in Photosynthesizing Cells of C3 Higher Plants

“…Gene expression of all β family CAs has been demonstrated in Arabidopsis thaliana leaves [10,12], as well as the expression of three α family genes encoding α-CA1, α-CA2 and α-CA3 [10]. Rudenko et al [13] did not detect expression of the latter, but demonstrated that arabidopsis leaves contain At4g20990 gene transcripts encoding α-CA4 found among thylakoid membrane proteins [14]. In arabidopsis, there are 6 active β-ca genes, and excepting β-ca3 the others have from 2 to 5 forms, resulting from alternative splicing predominantly in untranslated regions of one or two exons by the 3’ ends, and more often, by the 5’ ends of the corresponding RNAs.…”