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This study demonstrates that plants respond to competition from neighboring vegetation by transporting the HY5 transcription factor from shoots to roots, where it suppresses lateral root growth. Using live-imaging microscopy with shoot-specific inducible lines, researchers tracked HY5 movement through the phloem over 24 hours and showed that far-red light perception in shoots increases HY5 production and transport to roots. The experiments confirm that shoot-expressed HY5 is both necessary and sufficient to trigger root developmental changes in response to aboveground light competition signals.
Why it matters
Understanding how plants coordinate above- and below-ground growth in response to competition could inform agricultural strategies for optimizing crop density and resource allocation. This research reveals a fundamental mechanism of long-distance signaling in plants that could potentially be manipulated to improve crop resilience and yield in crowded growing conditions.
Understand the Science
⚠️ Preprint – Noch nicht peer-reviewed
Dieser Artikel wurde noch nicht von unabhängigen Experten begutachtet. Die Ergebnisse sind vorläufig und sollten mit Vorsicht interpretiert werden.
Plants perceive competitors through the reflection of Far-Red light from neighbouring leaves. A decrease in the Red: Far-red light ratio (R:FR) is perceived by phytochrome photoreceptors and triggers elongation responses aboveground, allowing plants to anticipate future competition for light; their primary energy source. However, low R:FR perception by the shoot also prompts an alteration of root development, possibly to conserve resources. An important regulator of this response is the bZIP transcription factor ELONGATED HYPOCOTYL 5 (HY5), which can be transported from the shoot to the root, where it suppresses auxin signaling and lateral root outgrowth. However, it remains unknown whether HY5 transport is the direct link between shoot-perceived low R:FR and a decrease in lateral root outgrowth. We therefore sought to uncover the mechanics and speed of HY5 transport. To this end, we constructed shoot-specific inducible lines to perform live-imaging of HY5 transport using a vertical confocal microscope. This allowed us to follow the transport and unloading of HY5 from the phloem into the protophloem pericycle, where it becomes nuclearly localized, in real time over a 24-hour period. To mimic plant competition, we applied supplemental FR light and observed that this increased the HY5 protein levels in the shoot and subsequent HY5 protein transport from shoot-to-root. Finally, we were able to show that shoot-expressed HY5 is necessary and sufficient to induce the root response to shoot perceived Far-Red light. This work showcases in detail how a small general transcription factor functions as a long-distance signal between shoot and root and integrates environmental signalling over long distances in the plant.