UV-B AND NITRIC OXIDE AS REGULATORS OF THE UVR8 SIGNALING PATHWAY

LATORRE, LUCAS; CASSIA, RAUL; LUKASZEWICZ, GERMÁN; FERNÁNDEZ, MARÍA BELÉN; CORREA-ARAGUNDE, NATALIA

Congreso; SAIB- SAMIGE Joint Meeting on line; 2020

The ultraviolet- B (UV-B) resistance locus 8 (UVR8) is the only known UV-B photoreceptor in plants. Upon UV-B irradiation, it turns from an inactive homodimer to an active monomer. In this form, UVR8 upregulates several genes involved in plant acclimation and tolerance to UV-B through the HY5 transcription factor (TF), and downregulate genes involved in growth through WRKY36, MYB73/77, BES1 and BIM1 TFs. Nitric oxide (NO) is an UV-B downstream gaseous signal that increases in response to UV-B and attenuates its damaging effects on plants. The aim of this work was to analyze the regulatory mechanisms of the UVR8 signaling pathway modulated by UV-B and NO. To this end, we used qRT-PCR to evaluate the expression of iaa19 (an auxin responsive gene), nia1 (nitrate reductase 1 involved in NO synthesis), phr1 (cyclobutane pirimidine dimers photolyase involved in DNA repair) and uvr8, in Arabidopsis thaliana WT and uvr8-1 null mutant under control or UV-B treatments (3.47 m−2 s−1, for 2h). Our results demonstrated that nia1 and phr1 were upregulated by UV-B whereas iaa19 and uvr8 were downregulated. Also, these responses were impaired in the uvr8-1 mutant, indicating that regulation of these genes involves the UVR8- dependent pathway. Iaa19 expression is repressed under UV-B due to MYB77, BIM1 and BES1 sequestration by UVR8. In silico analysis of the predicted uvr8 promoter showed binding motifs for these TFs. We have also analyzed chalcone synthase (chs) and uvr8 expression in tomato and maize plants. Chs was upregulated in both species after UV-B treatment. However, uvr8 was downregulated in maize under UV-B treatment, and upregulated in tomato. To explain these differences, we performed in silico analysis of the promoter regions. We also analyzed possible UV-B and NO co-regulation of the UVR8 signaling pathway components, using publicly available microarray and RNA-seq databases from Arabidopsis treated with NO. This analysis revealed that several genes involved in this pathway are also regulated by NO. We found that chs, iaa2 and GA2-oxidase (ga2ox) are upregulated in Arabidopsis leaves both by UV-B and exogenous application of NO. On the other hand, other genes were negatively co- regulated by UV-B and NO, such as the growth promoting genes pre1 (paclobutrazol resistance 1) and exp1 (expansin b 1). Finally, prediction analysis of S-nitrosylated proteins from the UVR8 signaling pathway and cysteine conservation using multiple sequence alignment revealed that COP1, PHR1, IAA14 and NIA1 could be targets of this post-translational modification. In conclusion, the components from the UVR8 signaling pathway may be regulated by NO both at the gene transcription and post-translational levels under UV-B irradiation.