PIF7 is a master regulator of thermomorphogenesis in shade

Abstract

The size of plant organs is highly responsive to environmental conditions. The plant’s embryonic stem, or hypocotyl, displays phenotypic plasticity, in response to light and temperature. The hypocotyl of shade avoiding species elongates to outcompete neighboring plants and secure access to sunlight. Similar elongation occurs in high temperature. However, it is poorly understood how environmental light and temperature cues interact to effect plant growth. We found that shade combined with warm temperature produces a synergistic hypocotyl growth response that dependent on PHYTOCHROME-INTERACTING FACTOR 7 (PIF7) and auxin. This unique but agriculturally relevant scenario was almost totally independent on PIF4 activity. We show that warm temperature is sufficient to promote PIF7 DNA binding but not transcriptional activation and we demonstrate that additional, unknown factor/s must be working downstream of the phyB-PIF-auxin module. Our findings will improve the predictions of how plants will respond to increased ambient temperatures when grown at high density.

MicroRNA156 conditions auxin sensitivity to enable growth plasticity in response to environmental changes in Arabidopsis

“…At both high and low temperatures, hypocotyl elongation due to the shade avoidance response can be effectively stimulated by the FR light reflected from neighboring plants 16 , 20 . An assay simulating the shade avoidance response is end-of-day FR (EOD-FR) treatment, in which a 15 min FR light treatment at the end of the daytime inactivates PHYB to promote hypocotyl growth during the nighttime.…”

“…An assay simulating the shade avoidance response is end-of-day FR (EOD-FR) treatment, in which a 15 min FR light treatment at the end of the daytime inactivates PHYB to promote hypocotyl growth during the nighttime. Like warm-temperature-dependent hypocotyl elongation, shade-induced hypocotyl elongation also relies on PIF-dependent auxin biosynthesis and signaling 16 , 20 . We thus asked whether miR156 is required for the auxin-dependent hypocotyl response by an EOD-FR treatment.…”

“…To avoid the complex influence of the blue light photoreceptor CRY1 on thermomorphogenesis 14,46 , we measured the daytime temperature response under continuous monochromatic R light 14,17 . Because thermomorphogenesis is mediated prominently by three bHLH transcription factors, PIF4, PIF5, and PIF7 [13][14][15][16] , we used pif4-2 and pif457 as negative controls. Among the three miRNA biogenesis mutants, only hyl1-2 showed a dramatic defect in the temperature response, comparable to that of pif4-2 (Fig.…”

“…These results indicate that miR156 is also required for auxin sensitivity at lower temperatures. biosynthesis and signaling 16,20 . We thus asked whether miR156 is required for the auxin-dependent hypocotyl response by an EOD-FR treatment.…”

“…PHYB interacts directly with a family of basic helix-loop-helix transcription factors, known as PHYTOCHROME-INTERACTING FACTORs (PIFs), to control their stability and transcriptional activity 11,12 . The growth plasticity of the hypocotyl is regulated mainly by PIF4, 5, and 7 [13][14][15][16] . Warm temperatures promote the expression, accumulation, and activity of PIF4 and PIF7, which in turn activate genes associated with auxin biosynthesis and signaling [13][14][15]17,18 .…”