Step on a snake, it bites back. Step on a plant, it suffers in silence? Actually, no. Like animals, plants too have survival strategies to help them endure and recover from such accidents. In the plant world, being nibbled on by herbivores or damaged by harsh weather is routine. Untreated wounds are entry points for various pathogens that can cause infections. Upon injury, plants activate damage responses that help them enter defence mode until the wound heals.
A recent study from the National Centre for Biological Sciences gained new insights into how rice plants manage wounds and what it could mean for agriculture. When grass-like plants are wounded, they initially enter a defence stage, followed by a period of recovery and growth. This research provides crucial insights into a receptor that is essential for a rice plant’s defence, recovery and growth. Insect herbivores are one of the biggest enemies of rice plants. When insects attack, rice respond in several ways to deal with the damage. They trigger molecular pathways leading to localized cell death at the injury site to contain the damage, deposit callose at the wound site to close it, produce volatile substances to alert nearby plants about the attack, and secrete toxins to deter insects. The concentration of these chemicals varies with the severity of the injury. These defense mechanisms are universal to almost all plant species. Following this initial defence stage, the plant seals the wound site and promote further growth.
“Grass-like plants or monocots respond to wounding very distinctly in comparison to dicots, like trees. When a leaf on a tree is injured, it often falls off entirely because the entire leaf undergoes cell death and stops functioning. Monocots including rice, however, restrict cell death to injury sites and promote leaf growth and elongation. This strategy is remarkable especially given that monocots have faced different levels of herbivory throughout their evolution” says Chitthavalli Y. Harshith, the lead author of the study.
The team led by Dr. Shivaprasad, associate professor at NCBS, aimed at identifying the molecular secrets of wound response in rice. They investigated which genes are activated following injury and identified two key peptides: plant elicitor peptides (PEPs) and phytosulfokine (PSK). Immediately after a plant is injured, PEPs rush to the scene, reaching their peak levels and locking onto their receptors. This triggers an initial intense defence response. However, what makes rice particularly intriguing is its unique response following this initial defence. After the defense stage, dicot plants have the ability to regenerate various parts, including roots, from wounded sites. Monocots, however, follow a different strategy. They enter a phase of vigorous growth, driven by PSKs, which become highly active once the defense subsides. These peptides act as signals for the plant to shift its energy towards recovery and growth. Harshith and team employed cutting-edge computational techniques, including docking and biochemical experiments, and identified a growth-promoting receptor called OsPSKR. These receptors sense and respond to PSKs in rice.
The team noticed that the plant heavily relies on OsPSKR receptor for its survival. Through knock-out experiments they removed the genes that form OsPSKR. They observed in its absence, not only the plant growth was compromised, the defense responses ramped up. Suggesting that OsPSKR regulates the defense signals. As wound heals and immediate threat fades, PSKs and their interaction with OsPSKR become more active. The research team argues that this transition from defence to growth relies on OsPSKR receptors, which steadily increase as wound response advances, while PEP levels decrease. With the discovery of this new receptor pathway in rice, exciting possibilities emerge for combating and understanding insect herbivory, the most significant threat to rice as a crop pest. However, achieving a clear understanding of the precise molecular mechanisms involved remains a crucial next step.
This study was funded by DAE/DBT/DST and supported by NCBS-TIFR.
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