Crosslinking of Ribosomal Proteins to RNA in Maize Ribosomes by UV-B and Its Effects on Translation

Abstract

Ultraviolet-B (UV-B) photons can cause substantial cellular damage in biomolecules, as is well established for DNA. Because RNA has the same absorption spectrum for UV as DNA, we have investigated damage to this cellular constituent. In maize (Zea mays) leaves, UV-B radiation damages ribosomes by crosslinking cytosolic ribosomal proteins S14, L23a, and L32, and chloroplast ribosomal protein L29 to RNA. Ribosomal damage accumulated during a day of UV-B exposure correlated with a progressive decrease in new protein production; however, de novo synthesis of some ribosomal proteins is increased after 6 h of UV-B exposure. After 16 h without UV-B, damaged ribosomes were eliminated and translation was restored to normal levels. Ribosomal protein S6 and an S6 kinase are phosphorylated during UV-B exposure; these modifications are associated with selective translation of some ribosomal proteins after ribosome damage in mammalian fibroblast cells and may be an adaptation in maize. Neither photosynthesis nor pigment levels were affected significantly by UV-B, demonstrating that the treatment applied is not lethal and that maize leaf physiology readily recovers.The evolution of terrestrial life was made possible by formation of a stratosphere that screens solar UV radiation, absorbing UV-C (,280 nm) and the most energetic UV-B (280-315 nm). Recent depletion of stratospheric ozone by chlorofluorocarbons and other pollutants has increased terrestrial UV-B levels with potentially deleterious consequences for all living organisms and particularly for plant development and physiology (Ballaré et al., 2001;Searles et al., 2001;Paul and Gwynn-Jones, 2003). In response to the inevitable exposure to damaging terrestrial UV-B, plants have evolved UV-induced mechanisms of protection and repair, such as accumulation of UVabsorbing pigments and use of UV-A photons to repair UV-B induced DNA damage (Stapleton and Walbot, 1994;Britt, 1996). Because of its absorption spectrum, DNA is a major target of UV-B radiation (Britt, 1996). This radiation can also damage proteins and lipids directly (Gerhardt et al., 1999); RNA molecules strongly absorb UV-B, but less is known about UV-B mediated damage to this cellular constituent.Experimentally, UV has been extensively used to analyze ribosome structure in vitro, because crosslinks can be introduced at points of close contact between proteins, within ribosomal RNA (rRNA), and between proteins and rRNA, tRNA, or mRNA Noah et al., 2000). Furthermore, in vivo crosslinks are generated in rRNA by UV treatment of bacterial cells (Stiege et al., 1986). In mammalian cells, UV-C and UV-B cause specific damage to the 3#-end of the 28S rRNA activating a response called ribotoxic stress (Iordanov et al., 1997(Iordanov et al., , 1998. Protein synthesis in plant cells is also sensitive to UV-C. Murphy et al. (1973) demonstrated that 254 nm radiation disrupted amino acid incorporation into protein in a wheat germ in vitro synthesis reaction and that the most sensitive target was mRNA. Subsequent studies in cult...

Plant L10 Ribosomal Proteins Have Different Roles during Development and Translation under Ultraviolet-B Stress

“…5A; Supplemental Fig. S4), in agreement with results obtained in experiments with maize plants exposed under UV-B radiation (Casati and Walbot, 2004). rpl10C and rpl10B mutant plants did not show significant differences in protein synthesis under control and UV-B exposure conditions compared with wild-type plants (Fig.…”

“…In a previous work, we found that UV-B radiation induces ribosomal damage, which occurs via formation of cross-links between RNA and specific ribosomal proteins, resulting in a 50% reduction in protein synthesis (Casati and Walbot, 2004). To study the role of RPL10 isoforms in translation, and their participation in translation under UV-B stress, we performed in vivo labeling of leaf proteins with [ 35 S]Met in control plants (no UV-B) and after exposure under UV-B radiation for 4 h (4 h UV-B).…”

“…The reduction of the ozone layer in the stratosphere has increased the terrestrial UV-B levels, with deleterious consequences for all organisms (Ballaré et al, 2001;Searles et al, 2001;Paul and Gwynn-Jones, 2003). The increase in transcription of translation-related genes is probably the consequence of ribosomal damage by UV-B, which occurs via the formation of cross-links between RNA and specific ribosomal proteins, resulting in a 50% reduction in protein synthesis (Casati and Walbot, 2004). Cellular recovery is accompanied by selective transcription and translation of ribosomal proteins and translation factors (Casati and Walbot, 2004).…”

“…The increase in transcription of translation-related genes is probably the consequence of ribosomal damage by UV-B, which occurs via the formation of cross-links between RNA and specific ribosomal proteins, resulting in a 50% reduction in protein synthesis (Casati and Walbot, 2004). Cellular recovery is accompanied by selective transcription and translation of ribosomal proteins and translation factors (Casati and Walbot, 2004). To further investigate the role of ribosomal proteins in UV-B responses, in particular the participation of RPL10 under conditions of UV-B stress, and to investigate if RPL10 proteins in plants have similar roles in development as described in other species, we studied the family of maize and Arabidopsis RPL10 genes.…”

ANTI-SILENCING FUNCTION1 Proteins Are Involved in Ultraviolet-Induced DNA Damage Repair and Are Cell Cycle Regulated by E2F Transcription Factors in Arabidopsis

“…Plants, because of their sessile condition and their requirement of sunlight for photosynthesis, are inevitably exposed to UV-B radiation (290-315 nm), which causes direct damage to DNA, proteins, lipids, and RNA (Britt, 1996;Jansen et al, 1998;Gerhard et al, 1999;Casati and Walbot, 2004a). Thus, plants have not only developed mechanisms that filter or absorb UV-B to protect them against DNA damage (Mazza et al, 2000;Bieza and Lois, 2001) but also have different DNA repair systems to remove or tolerate DNA lesions (Hays, 2002;Bray and West, 2005;Kimura and Sakaguchi, 2006).…”