Progressive alterations in UV-B induced phototropism during Arabidopsis development

VANHAELEWYN, L; SERRANO, A; VICZIAN, A; BERNULA, P; PRINSEN, E; ARANA, MV; BALLARE, C; VAN DER STRAETEN, D; VANDENBUSSCHE, F

Honalulu, Hawaii

Congreso; Plant Biology; 2017

Low fluence rate Ultraviolet-Blight (280-215nm) substantially affects plant morphology. Numerous UV-B inducedmorphological adaptations in Arabidopsis are ascribed to the UV-B specificphotoreceptor UV RESISTANCE LOCUS 8 (UVR8). Well documented examples are shorterpetioles and shorter stems. UVR8-mediated responses are also observed at thecellular level such as changes in cell elongation, division anddifferentiation. Notwithstanding this extensive awareness of UVR8 action ingrowth and development, there still remains a gap in our understanding onmultiple aspects of how plant architecture is controlled by UV-B. Our recent Arabidopsisresearch revealed that unilateral UV-B radiation can induce reorientation ofetiolated hypocotyls trough UVR8 mediated signaling. The effect of UVR8 onhypocotyls is independent of the action of phototropins. This response occurswith unilateral wavelengths shorter than 340nm, and shows a distinct kineticsthan phototropin mediated phototropic bending. The analysis of the kinetics of theplant reorientation allowed us to quantify the relative contribution of UVR8and phototropins in steering this UV-B induced phototropic movement ofetiolated hypocotyls. This data showed that in etiolated seedlings, there is a hierarchicalaction of phototropins and UVR8 action, with phototropins being more sensitiveto UV-B for regulating phototropism than UVR8 and therefore masking the effectof UVR8. In UV-B, phototropin signaling is mechanistically similar to that inblue light, involving phototropin autophosphorylation and NPH3dephosphorylation. Furthermore, the REPRESSOR OF UV-B PHOTOMORPHOGENESIS-mediatednegative feedback pathway is preventing UVR8-mediated signaling to allow fastphototropin-dependent bending. The UVR8-phototropinrelation as seen in hypocotyls, is not universally applicable. We found that themain photoreceptor for UV-B phototropism in inflorescence stems is UVR8, with aless significant role for phototropins. The role of different cell layers inUVR8 signaling is currently under exploration. Based on pharmacological assays,mutant analysis and reporter lines, this shifting role of UVR8 and phototropinsduring plant development will be presented and discussed.