In the past, Ultraviolet B (UV-B) was mainly documented as a stress factor, yet now it is wellknown

that UV-B light affects plant morphology and metabolism through a specific UV-B

photoreceptor pathway (UVR8). In the model dicot plant Arabidopsis, UV-B inhibition of

elongation and cell expansion yields small, compact plants. A large portion of this response is

mediated by UVR8. Although, a role for the plant hormone auxin has been documented

extensively, gibberellins (GA) and brassinosteroids (BR) have been respectively far less or totally

not been studied in this context.

The main objective of this project is to identify crucial downstream components of the UV-B

induced pathway that lead to growth inhibition and to interpret the larger context of mechanisms

that steer UV-B controlled growth. We will attempt to understand the possible role of growth

regulatory bHLH factors in the photomorphogenic UV-B response. Many growth promoting bHLH

factors are under the control of the elongation stimulating hormones BR and GA. At this moment it

is unknown whether and how UV-B impacts on BR and/or GA controlled growth or on growth

regulating bHLH genes. We therefore propose to perform research on a potential physiological link

between UV-B growth regulation and the BR/GA metabolism, signalling and responses.