As sessile organisms, plants have evolved complex defense systems against herbivores for successful survival and reproduction. Plant defense involves a metabolic cost where a tradeoff occurs between defense and growth. Plants may encounter the pathogen infection and herbivore attack during development. Immunosenescence is a common phenomenon in animals, but little is known about the variation of plant abilities against herbivores with age. Do plants have similar immunosenescence observed in animals?

The research group led by Prof. CHEN Xiaoya and MAO Yingbo at Shanghai Institute of Plant Physiology and Ecology of Chinese Academy of Sciences elucidated the mechanism of age-regulated dynamics of plant insect resistance. The paper entitled "Jasmonate response decay and defense metabolite accumulation contributes to age-regulated dynamics of plant insect resistance" has been published in Nature Communications.

Jasmonate (JA) plays important roles in plant reaction against chewing insects and it is called "defense phytohormone". Researchers found that the JA response is decayed but the insect resistance is enhanced along with plant growth. How is this opposite and complementary tendency controlled?

A small regulatory RNA, named miR156, is found by researchers to temporally modulate the output of JA signals. In the plants, miR156 functions as a key regulator of age-dependent development through targeting a group of transcription factors called SQUAMOSA PROMOTER BINDING PROTEIN-LIKE (SPL). SPL can interact with JA ZIM-domain (JAZ) proteins, the main repressor of JA signaling pathway. As SPL level gradually increases with age due to miR156 declining, JAZ proteins accumulate and the JA response is attenuated. However, despite the decay in JA response, older plants are comparatively more resistant to insect herbivores due to increased accumulation of glucosinolates, the major insecticide metabolites in Brassicaceae.

Researchers propose a model whereby constitutive accumulation of defense compounds plays a role in compensating for age-related JA-response deterioration during plant maturation. This discovery not only reveals the ingenious mechanism of insect resistant in plants but also help design more effective and reasonable pest control strategies.