Post‐transcriptional mechanisms control catalase synthesis during its light‐induced turnover in rye leaves through the availability of the hemin cofactor and reversible changes of the translation efficiency of mRNA

Abstract

SummaryThe enzyme catalase is light-sensitive. In leaves, losses caused by photoinactivation are replaced by new enzyme and the rate of de novo synthesis must be rapidly and¯exibly attuned to¯uctuating light conditions. In mature rye leaves, post-transcriptional mechanisms were shown to control the rate of catalase synthesis. The amount of the leaf catalase (CAT-1) transcript did not increase with light intensity, but was even higher after dark exposure of light-grown leaves. Initiation was apparently not limiting translation in the dark, as the association of the Cat1 mRNA with polysomes did not change notably under different light conditions. By analysing the translation of catalase polypeptides in cell-free systems with poly(A)+ RNA from leaves or with mRNA transcribed from a Cat1-containing cDNA clone, two mechanisms of post-transcriptional control were identi®ed. First, translation of catalase depended on the presence of hemin. In leaves, the availability of hemin may signal the extent of catalase degradation as the hemin of the inactivated enzyme is recycled. Second, the translation ef®ciency of the Cat1 transcripts was reversibly modulated in a dose-dependent manner by the light intensity to which leaves were exposed, prior to extraction. The Cat1 mRNA from light-exposed leaves was translated much more ef®ciently than mRNA from dark-exposed leaves. The increase of its translation activity in vivo was not blocked by cordycepin but was suppressed by methylation inhibitors, indicating a reversible modi®cation of pre-existing mRNA by methylation. Translation of in vitro synthesized Cat1 mRNA required a methylated cap (m7GpppG), but was virtually below detection when it contained an unmethylated cap (GpppG).

Availability of Rubisco Small Subunit Up-Regulates the Transcript Levels of Large Subunit for Stoichiometric Assembly of Its Holoenzyme in Rice

“…For example, protein synthesis of Rubisco rapidly declined when illuminated amaranth (Amaranthus hypochondriacus) seedlings were transferred to dark conditions (Berry et al, 1988). Light intensity did not affect polysome loading of the leaf catalase mRNA in rye (Secale cereale; Schmidt et al, 2002), although its protein turnover rate increased in a dose-dependent manner along with light intensity (Hertwig et al, 1992). In these cases, it has been suggested that translational initiation and elongation are modulated in a coordinated manner.…”

Redox Regulation in Photosynthetic Organisms: Signaling, Acclimation, and Practical Implications

“…The lack of strong ROS induction of many antioxidant genes in plants may also reflect the importance of regulation of the antioxidant system at the post-transcriptional level (264,316,366). Many true antioxidant genes are quite strongly expressed even in nonstress conditions, either to deal with the high rates of constant ROS production that occur during photosynthesis, photorespiration, and respiration ( Fig.…”

Effects of lead (PB) and cadmium (CD) elements on lipid peroxidation, catalase enzyme activity and catalase gene expression profile in tomato plants

“…The results suggest that a translationalposttranslational level of control for CAT gene expression or enzyme activity might be regulated by the reversible modulation of the functionality of its mRNA, depending on the supply of the methyl group donors from glycine and serine and that production of these amino acids is greatly enhanced by photo respiratory carbon flow. Therefore, catalase protein synthesis is associated with the photo respiratory and photosynthetic pathways (Schmidt et al 2002).…”