Plants' responses to Ultra Violet-B radiation
Author: Dhammaprakash P. Wankhede
ICAR-National Bureau of Plant Genetic Resources, Pusa campus, New Delhi
Ultra-violet B (UV-B, 280–320 nm) radiation is a small component of minor component of the solar spectrum and is strongly absorbed by ozone in stratosphere. However, depletion of the ozone layer has led to an increasing amount of UV-B radiation at the earth’s surface. Higher level of UV-B has several harmful consequences for all living beings. Increased UV-B level have several physiological as well as morphological changes such as, reduced plant growth, shortened internodes, and thicken the wax of leaves and cuticular wax, thus, significantly impact agricultural ecosystems (Teramura and Sullivan, 1994; Jansen et al., 1998; Paul and Gwynn-Jones, 2003). UV-B has been shown to induce changes in secondary metabolites, which in turn affects numerous physiological processes. UV-B also induces accumulation of phenolic compounds (UV absorbing compounds) such as flavonoids, and lignin, sinapate esters etc. which as free radical scavengers reduces deleterious effects of irradiation (Rozema et al., 1997). These compounds have direct relation to resistance against higher levels of UV. It has been observed that mutants which fail to accumulate these compounds show hypersensitivity to UV-B radiation, and mutants with higher flavonoid and sinapate concentrations show increased resistance to UV radiation (Li et al., 1993; Jin et al., 2000; Bieza and Lois, 2001).
Nature of the response to UV-B is also dependent on the fluence rate, duration, and wavelength of the UV-B treatment (Brosche and Strid, 2003; Frohnmeyer and Staiger, 2003; Ulm and Nagy, 2005). In general, exposure to high fluence rates and short wavelengths of UV-B is likely to cause stress responses and possibly necrosis. Among the known damages are damage to DNA, proteins, membrane lipids and adverse effect on protein synthesis and photosynthetic reactions. A low fluence rate of UV-B, however, induces regulatory responses in plants. For example, lower levels of UV-B inhibit stem extension, stimulate cotyledon opening, promote the accumulation of flavonoids and regulate the expression of a range of genes (reviewed by Jenkins, 2009). These low fluence UV-B induced regulatory responses may not be stress responses, and are likely to be photomorphogenic in nature, comparable to responses mediated by phytochromes, cryptochromes and phototropins.
Differential gene expression in response to UV-B
A common feature of UV-B induced responses is transcriptional activation or repression of genes upon perception of an external stimulus (Yang et al., 1997). Several genes are known to have altered expression in response to UV-B (Brown et al., 2005; Xu et al., 2006; Brown and Jenkins, 2008). Different types of UV-B exposure regulate different sets of genes (Brosche et al., 2002, Brown and Jenkins, 2008). High fluence rates and short wavelengths of UV-B induce many genes normally expressed in defence, wound or general stress responses (A-H-Mackerness, 2000; Ulm and Nagy, 2005) whereas, low fluence rates shorter exposures and longer wavelengths of UV-B leads to increased expression of several genes involved in UV protection (Frohnmeyer et al., 1999; Jenkins et al., 2001). Transcriptomic studies in maize (Casati et al., 2006) and Arabidopsis (Ulm and Nagy, 2005) show that UV-B regulates a large number of genes concerned with a wide range of cellular processes. In C. roseus, UV induced transcription of genes encoding tryptophan decarboxylase (Tdc), strictosidine synthase (Str) and Mitogen activated protein kinase (CrMPK3) have been observed (Raina et al., 2011, Ramani et al., 2007).
In rice, suppression subtractive hybridization between two rice genotypes, UV-B-resistant-Lemont and the UV-B sensitive-Dular upon UV-B irradiation revealed differential expression of several genes related to defence responses. The genes encoding HECT domain-containing protein, ascorbate peroxidase, receptor-like protein kinase, ubiquitin carrier protein (Rad6), phenylalanine ammonialyase, 4-coumarate, CoA ligase and chalcone synthase showed enhanced expression to different degrees in two rice cultivars (Fang et al., 2009). Additionally, UV induced expression of different phytoalexin biosynthetic genes like OsKS4 (Kaurene senthase 4) is known (Shimura et al., 2007). UV induced expression of Mitogen Activated Protein Kinase cascade genes have also been shown in rice (Wankhede et al. 2013, 2016).
UV-B responsive expression of several genes triggered the initiation of studies for identification of promoter elements and transcription factors involved in these responses. Further, attempts have been made to understand how transcriptional regulation is coupled to UV-B signalling pathways. Detailed studies of DNA sequence elements that regulate transcription of the gene encoding the key flavonoid biosynthesis enzyme chalcone synthase (CHS) did not identify any UV-B-specific element (Kaiser et al., 1995; Hartmann et al., 1998). However, a UV-B-specific element was identified recently in the Arabidopsis ANAC13 gene, which encodes a putative NAC-domain transcription factor (Safrany et al., 2008). This element is necessary for induction by shorter wavelength, higher-fluence rate UV-B.
A majority of genes induced by UV-B encode transcription factors (Kilian et al., 2007) play key roles in UV-B responses. A few transcription factors which show UV induced expression are also involved in regulation of biosynthesis of UV protective phenolic compounds (Cominelli et al., 2008). The Arabidopsis basic leucine-zipper transcription factor ELONGATED HYPOCOTYL 5 (HY5) is required for the UV-B induction of a substantial number of genes including those with vital roles in UV protection (Brown et al., 2005). A few members of rice WRKY gene family also show UV-B inducible expression viz OsWRKY89 (named as WRKY101 by Zhang and Wang, 2005) in addition to MeJA, and infection by blast fungus M. grisea (Wang et al., 2007).
A-H-Mackerness S. (2000) Plant responses to UV-B (UV-B: 280–320 nm) stress: What are the key regulators? Plant Growth Regul 32, 27–39.
Bieza K, Lois R. (2001) An Arabidopsis mutant tolerant to lethal ultraviolet B level shows constitutively elevated accumulation of flavonoids and phenolics. Plant Physiol 126, 1105–1115.
Brosche M, Schuler MA, Kalbina I, Connor L, Strid A. (2002) Gene regulation by low level UV-B radiation: identification by DNA array analysis. Photochem Photobiol Sci 1, 656–64.
Brosche M, Strid A. (2003) Molecular events following perception of ultraviolet-B radiation by plants. Physiol Plant 117, 1-10.
Brown BA, Cloix C, Jiang GH, Kaiserli E, Herzyk P, Kliebenstein DJ, Jenkins GI. (2005) A UV-B-specific signaling component orchestrates plant UV protection. Proc Natl Acad Sci USA 102, 18225–18230.
Brown BA, Jenkins GI. (2008) UV-B signalling pathways with different fluence-rate response profiles are distinguished in mature Arabidopsis leaf tissue by requirement for UVR8, HY5, and HYH. Plant Physiol 146, 576–88.
Casati P, Stapleton AE, Blum JE, Walbot V. (2006) Genome-wide analysis of high-altitude maize and gene knockdown stocks implicates chromatin remodeling proteins in response to UV-B. Plant J 46, 613–27.
Cominelli E, Gusmaroli G, Allegra D. et al. (2008). Expression analysis of anthocyanin regulatory genes in response to different light qualities in Arabidopsis thaliana. J Plant Physiol 165, 886–94.
Fang CX, Wu XC, Zhang HL, Jun X, Wu WX, Lin WX. (2009) UV-induced differential gene expression in rice cultivars analysed by SSH Plant Growth Regul 59, 245–253.
Frohnmeyer H, Staiger D. (2003) Ultraviolet-B radiation-mediated responses in plants. Balancing damage and protection. Plant Physiol 133, 1420-28.
Frohnmeyer H, Loyall L, Blatt MR, Grabov A. (1999) Millisecond UV-B irradiation evokes prolonged elevation of cytosolic-free Ca2+ and stimulates gene expression in transgenic parsley cell cultures. Plant J 20, 109-17.
Hartmann U, Valentine WJ, Christie JM, Hays J, Jenkins GI, Weisshaar B. (1998) Identification of UV/blue light-response elements in the Arabidopsis thaliana chalcone synthase promoter using a homologous protoplast transient expression system. Plant Mol Biol 36, 741-54.
Jansen MAK, Gaba V, Greenberg BM. (1998) Higher plants and UVB radiation: balancing damage, repair and acclimation. Trends Plant Sci 3, 131–135.
Jenkins GI, Long JC, Wade HK, Shenton MR, Bibikova TN. (2001) UV and blue light signalling: pathways regulating chalcone synthase gene expression in Arabidopsis. New Phytol 151, 121-31.
Jenkins IG. (2009) Signal transduction in responses to UV-B radiation Annu Rev Plant Biol 60, 407-31.
Jin H, Cominelli E, Bailey P, Parr A, Mehrtens F, Jones J, Tonelli C, Weisshaar B, Martin C. (2000) Transcriptional repression by AtMYB4 controls production of UV-protecting sunscreens in Arabidopsis. EMBO J 19, 6150-6161.
Kaiser T, Emmler K, Kretsch T,Weisshaar B, Schafer E, Batschauer A. (1995) Promoter elements of the mustard CHS1 gene are sufficient for light regulation in transgenic plants. Plant Mol Biol 28, 219-29.
Kilian J, Whitehead D, Horak J. et al. (2007) The AtGenExpress global stress expression data set: protocols, evaluation and model data analysis of UV-B light, drought and cold stress responses. Plant J 50, 347-63.
Li J, Ou-Lee T, Raba R, Amoundson R, Last R. (1993) Arabidopsis flavonoid mutants are hypersensitive to UV-B irradiation. Plant Cell 5, 171-179.
Paul ND, Gwynn-Jones D. (2003) Ecological roles of solar UV radiation: towards an integrated approach. Trends Ecol Evol 18, 48-55.
Ramani S, Chelliah J. (2007) UV-B-induced signaling events leading to enhanced-production of catharanthine in Catharanthus roseus cell suspension cultures. BMC Plant Biol 7, 61-77.
Raina SK, Wankhede DP, Jaggi M, Singh P, Jalmi SK, Raghiram B, Sheikh AH, Sinha AK (2012) CrMPK3, a mitogen activated protein kinase from Catharanthus roseus and its possible role in stress induced biosynthesis of monoterpenoid indole alkaloids. BMC Plant Biol 12:134
Rozema J, van de Staaij J, Bjorn LO, Caldwell M. (1997) UV-B as an environmental factor in plant life: stress and regulation. Trends Ecol Evol 12, 22-28.
Safrany J, Haasz V, Mate Z. et al. (2008) Identification of a novel cis-regulatory element for UV-B-induced transcription in Arabidopsis. Plant J 54, 402-14.
Shimura K, Okada A, Okada K. et al. (2007) Identification of a biosynthetic gene cluster in rice for momilactones. J Biol chem 282 (47), 34013-34018.
Teramura AH, Sullivan JH. (1994) Effects of UV-B radiation on photosynthesis and growth of terrestral plants. Photosynth Res 39, 463-473.
Ulm R, Nagy F. (2005) Signalling and gene regulation in response to UV light. Curr Opin Plant Biol 8, 477-82.
Wang H, Hao J, Chen X, Hao Z Wang A Lou Y, Peng Y, Guo Z. (2007) Overexpression of rice WRKY89 enhances ultraviolet B tolerance and disease resistance in rice plants. Plant Mol Biol 65, 799-815.
Wankhede DP, Kumar K, Singh P, Sinha AK (2013) Involvement of mitogen activated protein kinase kinase 6 in UV induced transcripts accumulation of genes in phytoalexin biosynthesis in rice. Rice 6:35.
Wankhede DP, Singh P, Jaggi M, Rao KP, Raina SK, Sinha AK (2013) Involvement of mitogen activated protein kinase kinase 6 in UV induced transcripts accumulation of genes in phytoalexin biosynthesis in riceJ. Plant Biochem. Biotechnol.DOI 10.1007/s13562-016-0351-0
Xu X, Chen C, Fan F, Chen Z. (2006) Physical and functional interactions between pathogen-induced Arabidopsis WRKY18, WRKY40, and WRKY60 transcription factors. Plant Cell 18, 1310-1326.
Yang Y, Shah J, Klessig DF. (1997) Signal perception and transduction in plant defense response. Genes Dev 11, 1621-1639.
Zhang Y, Wang L. (2005) The WRKY transcription factor superfamily: its origin in eukaryotes and expansion in plants. BMC Evol Biol 5, 1-12.
About Author / Additional Info:
Scientist, Division of Genomic Resources, ICAR-National Bureau of Plant Genetics Resources, New Delhi , India
Trending Articles ( Receiving maximum views in the last few days )