Recently, cooperating with South China Agricultural University, researchers from Biotechnology Research Institute in CAAS have published a research paper entitled “Arabidopsis FHY3 and FAR1 Regulate the Balance between Growth and Defense Responses under Shade Conditions”on July 17 in Plant Cells. This study revealed the molecular mechanism of plant growth and defense response in shade conditions by fusing photosensitive pigments and jasmonic acid signaling pathways.

Increasing crop yield per unit area can be achieved by increasing planting density. However, high-density planting could trigger shade avoidance responses, which cause exaggerated growth and increased susceptibility to various diseases. Previous studies have shown that the rapid elongation of plants under shade (i.e., reduced red to far-red ratios) is regulated by phytochromes and various phytohormones. However, the detailed molecular mechanisms governing the interaction among these signaling pathways are not well understood.

This study reported that loss-of-function mutants of FAR-RED ELONGATED HYPOCOTYL3 (FHY3) and FAR-RED-IMPAIRED RESPONSE1 (FAR1), which encode two homologous transcription factors essential for phytochrome signaling, exhibit an exaggerated shade avoidance phenotype. FHY3 and FAR1 repress plant growth through directly activating the expression of two atypical basic helix-loop-helix transcriptional co-factors PHYTOCHROME RAPIDLY REGULATED1 (PAR1) and PAR2, and that this process is antagonized by a group of JASMONATE ZIM-DOMAIN (JAZ) proteins, key repressors of the jasmonic acid (JA) signaling pathway, through physical interactions. Further, FHY3 interacts with MYC2, a key transcriptional regulator of JA responses, coordinately regulating JA-responsive defense gene expression. This study unveil a previously unrecognized mechanism whereby plants balance their growth and defense responses through convergence of the phytochrome signaling pathway and JA signaling pathway under shade conditions.

Increasing planting density is an effective means of increasing crop yield per unit land area, which requires the breeding and utilization of shade-tolerant crop cultivars that can balance their growth and defense. This study will help breeders to use this knowledge to guide breeding of shade-tolerant crop plants.

This research was funded by the National Natural Science Foundation of China (31500239, 31430008).

By LiuYang (liuyang06@caas.cn)