Plant growth regulation in a changing climate

Unlike animals, most plant organs arise after seed germination. Being sessile, the size and shape of these organs are in turn optimized to the local environment. The embryonic stem of the plant, or hypocotyl, is one such organ that displays impressive phenotypic plasticity, and its length is affected both by light and temperature. In response to foliar shade and high temperature, the hypocotyl of Arabidopsis plants grows taller. Previous studies have shown that this response is mediated by a family of transcription factors called PIFs, with different PIFs having greater roles to play in each of the two environmental conditions. However, it is poorly understood how these environmental variables interact to affect plants at the morphological and molecular levels. Here, we ask what will be the response to shade under warmer temperature. We found that the effect on hypocotyl growth was synergistic and resulted in very long hypocotyls relative to each individual environmental condition. Shade and high-temperature treatment resulted in increased PIF activity, leading to amplification of the plant’s response to the growth hormone auxin, resulting in hypocotyl elongation. Interestingly, this response was also found to be dependent on the heat shock protein 90 (HSP90). Shade responses are known to negatively affect the yield and quality of some crop species, and our findings might improve our predictions of how crops will respond to increased temperatures when grown at high density, a condition in which mutual shading occurs.