Role of root UV-B sensing in Arabidopsis early seedling development

Abstract

All sun-exposed organisms are affected by UV-B [(UVB) 280 -320 nm], an integral part of sunlight. UVB can cause stresses or act as a developmental signal depending on its fluence levels. In plants, the mechanism by which high-fluence-rate UVB causes damages and activates DNA-repair systems has been extensively studied. However, little is known about how nondamaging low-fluencerate UVB is perceived to regulate plant morphogenesis and development. Here, we report the identification of an Arabidopsis mutant, root UVB sensitive 1 (rus1), whose primary root is hypersensitive to very low-fluence-rate (VLF) UVB. Under standard growth-chamber fluorescent white light, rus1 displays stunted root growth and fails to form postembryonic leaves. Experiments with different monochromatic light sources showed that rus1 phenotypes can be rescued if the seedlings are allowed to grow in light conditions with minimum UVB. We determined that roots, not other organs, perceive the UVB signal. Genetic and molecular analyses confirmed that the root light-sensitive phenotypes are independent of all other known plant photoreceptors. Three rus1 alleles have been identified and characterized. A map-based approach was used to identify the RUS1 locus. RUS1 encodes a protein that contains DUF647 (domain of unknown function 647), a domain highly conserved in eukaryotes. Our results demonstrate a root VLF UVB-sensing mechanism that is involved in Arabidopsis early seedling morphogenesis and development.

Impact of UV-B on drought- or cadmium-induced changes in the fatty acid composition of membrane lipid fractions in wheat

“…Mutant plant genotypes with impaired flavonoid biosynthesis are more susceptible to damage by UV-B (Kaiserli and Jenkins, 2007). Interestingly, in Arabidopsis it was found that the roots, rather than other organs, perceive the UV-B signal (Tong et al, 2008). In the present study flavonoid content was influenced to the greatest extent by UV-B and PEG alone, while in the roots, besides the expected effect of Cd, UV-B stress was also detected.…”

Arabidopsis STO/BBX24 negatively regulates UV-B signaling by interacting with COP1 and repressing HY5 transcriptional activity

“…The increased inhibition of primary root elongation in bbx24 seedlings is confined to UV-B, suggesting that BBX24 also plays a crucial role in UV-B-mediated inhibition of root elongation. Therefore, BBX24 and the recently identified RUS1 and RUS2 proteins for root UV-B response [25,26] represent part of the UV-B sensing machinery in Arabidopsis roots. The root elongation is significantly blocked in rus1-1 and rus2-1 mutants exclusively under very-low-fluence UV-B [25,26].…”

“…Therefore, BBX24 and the recently identified RUS1 and RUS2 proteins for root UV-B response [25,26] represent part of the UV-B sensing machinery in Arabidopsis roots. The root elongation is significantly blocked in rus1-1 and rus2-1 mutants exclusively under very-low-fluence UV-B [25,26]. Interestingly, this phenotype of rus1-2 under UV-B is not correlated with the common UV-Bresponsive genes, such as CHS and HY5 [26], indicating that the UV-B signaling pathway in the root is different from that in the shoot.…”

The ArabidopsisTUMOR PRONE5Gene Encodes an Acetylornithine Aminotransferase Required for Arginine Biosynthesis and Root Meristem Maintenance in Blue Light

“…The very low effective light fluence rates that act on tup5-1 indicate a physiological relevance and suggest an as yet unknown connection between amino acid biosynthesis, light perception, and root development. Roots contain red and blue light photoreceptors that may perceive light directly (Sakamoto and Briggs, 2002;Galen et al, 2007;Costigan et al, 2011;Dyachok et al, 2011, and references therein) and also respond to UV-B (Tong et al, 2008). Our genetic analyses have largely excluded several known components from light signaling pathways (CRY1, PHYB, HY2, and HY5) to operate in the TUP5 pathway, but not all known light receptors that could have a function in light perception by roots have been tested.…”

“…Amino acid metabolism might also influence root meristem maintenance, as well as root growth and development, as was indicated by mutants of Asp and His biosynthesis (Miesak and Coruzzi, 2002;Mo et al, 2006). It is well documented that endogenous factors controlling root growth, such as phytohormones, are often regulated by exogenous signals, for example, by water and nutrient conditions (López-Bucio et al, 2003;Monshausen and Gilroy, 2009), as well as light (Canamero et al, 2006;Tong et al, 2008). There is evidence that roots contain different photoreceptors, that they are able to perceive light of different wavelengths, and that this regulates root functions (Sakamoto and Briggs, 2002;Canamero et al, 2006;Galen et al, 2007;Tong et al, 2008;Costigan et al, 2011;Dyachok et al, 2011, and references therein).…”