Beating the blues: engineering cryptochrome expression improves soybean yield

Phytochrome A overexpression can increase harvest index, as was shown 25 years ago in a breakthrough paper on tobacco ( Robson et al., 1996 ). The impact of this important discovery has, however, not been fully developed. Plants at high densities often respond strongly to nearby competitors by strong elongation of their internodes and upward bending of their leaves, i.e., shade avoidance. This is crucial for plants to ascertain access to sunlight, and this navigation through vegetation occurs through light cues that are sensed with various photoreceptors. A spectacular sensitivity is displayed by sun-loving plants that can already sense their nearby competitors even before mutual shading occurs and respond through a first acceleration of shoot elongation. This anticipatory response is triggered through red (R):far-red (FR) light-sensitive phytochrome photoreceptors that detect FR light that is reflected by nearby vegetation. When the vegetation continues to grow and true shading occurs, there is also a significant depletion of red and blue light, since the latter two are absorbed for photosynthesis in the overhead leaves (reviewed in Pierik and Ballaré, 2021 ). Plants can respond to blue light depletion, especially when integrating it with signaling of FR enrichment in Arabidopsis ( de Wit et al., 2016 ).