Dimming the lights (and defenses): Dim light decreases rice resistance against brown plant hopper insects

Sarah Courbier

Plant Physiol.; 2023 Feb 12; 191(2):837-839. doi: 10.1093/plphys/kiac529.

To date, increasing planting density has been the most effective way to boost crop yield per land area. However, at high density, plants eventually shade each other and suffer from a lack of light. Plants perceive shade signals, including dim light (reduced light intensity), through specific photoreceptors called phytochromes. Upon activation by light, phytochromes translocate from the cytoplasm to the nucleus where they negatively regulate growth responses. In contrast, the perception of shade signals inactivates phytochromes, thereby triggering rapid growth to outcompete neighboring vegetation; a process known as the shade avoidance syndrome

In Plant Physiology, Huang et al. (2022) investigated the effects of dim light on rice (Oryza sativa) resistance toward sap-sucking brown plant hopper (BPH) insects. They demonstrate that dim light compromises rice resistance against BPH by elevating ethylene biosynthesis and signaling in a phytochrome B (PHYB)-dependent manner.

The authors first investigated the effect of light intensity and light signaling components on rice resistance against BPH by subjecting plants to strong (650 µmol m⁻² s⁻¹), control (200 µmol m⁻² s⁻¹) or dim (50 µmol m⁻² s⁻¹) light for 24 h prior to insect infestation. Interestingly, strong light promoted plant resistance to BPH while dim light had the opposite effect. In addition, the aggravation of BPH symptoms by dim light was also observed in rice cultivars known to be BPH resistant, suggesting an urgency of redefining our current agriculture practices.

See https://academic.oup.com/plphys/article/191/2/837/6847271?login=false

Figure 1: A proposed model of how dim light conditions decrease rice resistance to BPH insects. In normal light conditions (left panel), light-activated OsPHYB translocates to the nucleus where it physically interacts with OsPIL14, thereby triggering OsPIL14 degradation and keeping ethylene biosynthesis and signaling low. In parallel, OsEBF1 interacts with OsEIL2, leading to OsEIL2 degradation, which renders plant resistance toward BPH. In dim light conditions (right panel), OsPHYB is inactivated and sequestrated in the cytoplasm, allowing OsPIL14 to bind the promoter of the ethylene biosynthesis gene OsACO1, resulting in increased ethylene levels and the up-regulation of OsEIL2. Meanwhile, the remaining nuclear-localized OsPHYB stabilizes OsEIL2 by competitively interacting with OsEBF1. The subsequent stabilization of OsEIL2 by OsPHYB leads to the activation of ethylene responses, resulting in compromised plant resistance to BPH. Illustration created with BioRender.com.