SHADE AVOIDANCE SIGNALLING IS AFFECTED BY DROUGHT STRESS IN A. THALIANA

SEMMOLONI, MARIANA; COSTIGLIOLO ROJAS, CECILIA; CASAL, JORGE J.

Salta

Congreso; LV Annual SAIB Meeting and XIV PABMB Congress; 2019

Sociedad Argentina de Investigación Bioquímica y Biología Molecular

Neighboring vegetation modifies the light environment by absorbing red and blue light whilst more efficiently transmitting and reflecting far-redlight. These cues are perceived mainly by the photo-sensory sensors phytochrome B (phyB) and cryptochrome 1 (cry1). Reduced phyB and cry1activity triggers a set of morphological changes, known as shade avoidance responses, which include the elongation of hypocotyls, stems andpetioles. The enhanced cellular growth that mediates these responses is mainly mediated by elevated signaling of the growth hormone auxin,induced by the transcription factors PHYTOCHROME INTERACTING FACTORs (PIFs), repressed by phyB and cry1 in the absence of shade.Integration of neighbor and other environmental cues on the control of plant growth is an emerging topic. Despite our profound knowledge ofthe mechanisms of perception and transduction of shade signals, whether shade avoidance is affected by water availability remains unclear. Toinvestigate this issue, we exposed seedlings of tomato, peas and Arabidopsis thaliana to the combination of light treatments simulating neighborcues and different levels of water availability. In all three species, water restriction impaired the shade-avoidance response. Mutations at thePIF3, PIF4, PIF5 and/or PIF7, which reduce the magnitude of shade-avoidance responses, also impaired the growth response to wateravailability. Several pieces of evidence indicate that water restriction did not simply limit growth at the biophysical level, by affecting cellularturgor pressure required for expansion. Rather, it affected signaling events involved in the shade-avoidance response. First, a meta-analysis ofpublished transcriptome data of Arabidopsis seedlings exposed to shade or drought treatments showed that the gene ontology term auxintransport was enriched among the genes induced by shade and repressed by drought. Since auxin-transport is required for shade avoidance,drought could affect this step of the response. Second, drought reduced the promotion of expression of shade-avoidance marker genes when bothtreatments were combined. Third, confocal microscopy of hypocotyl cells revealed that the promotion of PIF4 nuclear abundance by neighborcues was reduced by drought. In these cells, which are responsible for the growth response, drought reduced auxin signal as revealed by an auxinsensor in combination with confocal microscopy. We propose that drought inhibit shade avoidance by modulating signaling downstream thephoto-sensory receptors. These findings provide insight into the molecular mechanism of signal integration that contributes to adjust growthresponses to the complex environmental conditions that plants experience in the field.