The photomorphogenic factors UV-B RECEPTOR 1, ELONGATED HYPOCOTYL 5, and HY5 HOMOLOGUE are part of the UV-B signalling pathway in grapevine and mediate flavonol accumulation in response to the environment.

Rodrigo Loyola,Alvaro Peña-Neira,Jochen Bogs,José Antonio Alcalde,Darren Chern Jan Wong,Erika Cavallini,Alessandra Amato,Akifumi Azuma,Abraham Mas,Stefan Czemmel,Giovanni Battista Tornielli,Simone Diego Castellarin,José Tomás Matus,Janine Höll,Tobias Ziegler,Patricio Arce-Johnson,Felipe Aquea,Daniela Herrera

doi:10.1093/jxb/erw307

Abstract

Grapevine (Vitis vinifera L.) is a species well known for its adaptation to radiation. However, photomorphogenic factors related to UV-B responses have not been molecularly characterized. We cloned and studied the role of UV-B RECEPTOR (UVR1), ELONGATED HYPOCOTYL 5 (HY5), and HY5 HOMOLOGUE (HYH) from V. vinifera We performed gene functional characterizations, generated co-expression networks, and tested them in different environmental conditions. These genes complemented the Arabidopsis uvr8 and hy5 mutants in morphological and secondary metabolic responses to radiation. We combined microarray and RNA sequencing (RNA-seq) data with promoter inspections to identify HY5 and HYH putative target genes and their DNA binding preferences. Despite sharing a large set of common co-expressed genes, we found different hierarchies for HY5 and HYH depending on the organ and stress condition, reflecting both co-operative and partially redundant roles. New candidate UV-B gene markers were supported by the presence of HY5-binding sites. These included a set of flavonol-related genes that were up-regulated in a HY5 transient expression assay. We irradiated in vitro plantlets and fruits from old potted vines with high and low UV-B exposures and followed the accumulation of flavonols and changes in gene expression in comparison with non-irradiated conditions. UVR1, HY5, and HYH expression varied with organ, developmental stage, and type of radiation. Surprisingly, UVR1 expression was modulated by shading and temperature in berries, but not by UV-B radiation. We propose that the UV-B response machinery favours berry flavonol accumulation through the activation of HY5 and HYH at different developmental stages at both high and low UV-B exposures.

Highlights

Ultraviolet B radiation (UV-B; 280–315 nm) is a component of solar radiation and is harmful to all living organisms
Despite sharing a large set of common co-expressed genes, we found different hierarchies for HYPOCOTYL 5 (HY5) and HY5 HOMOLOGUE (HYH) depending on the organ and stress condition, reflecting both co-operative and partially redundant roles
Two general signalling pathways are present in Arabidopsis for responding to UV-B radiation (Jenkins, 2009): a non-specific pathway, produced by high levels of radiation causing direct DNA damage and release of reactive oxygen species (ROS); and a specific signalling pathway, mediated by photomorphogenic components which respond to low levels of UV-A and UV-B radiation

Summary

Introduction

Ultraviolet B radiation (UV-B; 280–315 nm) is a component of solar radiation and is harmful to all living organisms. We obtained the spatio-temporal expression of UVR1, HY5, and HYH in different organs and developmental stages of field-grown grapevine plants (Fig. 3).

Results

Conclusion