Seeds are vital for plant reproduction and agriculture. Seed size, a crucial trait for plant adaptation and crop yield, is intricately controlled by genetic signals and environmental factors. The plant hormone jasmonate (JA) is known to help plants respond to environmental challenges like pests and salt stress, but its specific role in regulating seed development remains unclear.

In a study published in The Plant Cell, researchers from Xishuangbanna Tropical Botanical Garden (XTBG) of the Chinese Academy of Sciences revealed a novel mechanism by which the plant hormone jasmonate controls seed size. They discovered that the jasmonate signaling pathway acts as a negative regulator of seed size in the model plant Arabidopsis thaliana.

Researchers revealed how the CORONATINE INSENSITIVE1 (COI1)-mediated jasmonate signaling pathway affected seed growth by inhibiting the expression of KLUH (KLU) gene, a key promoter of seed coat cell growth. They found that blocking jasmonate signaling resulted in significantly larger seeds, confirming jasmonate's role in limiting size. They also found that jasmonate signaling components were highly active in the seed coat during development.

Moreover, researchers explored the interaction between jasmonate ZIM-DOMAIN (JAZ) repressors and two transcription factors, SUPPRESSOR OF DA1-1 (SOD7) and DEVELOPMENT-RELATED PcG TARGET IN THE APEX4 (DPA4). They found that jasmonate signaling repressor protein JAZ interacted with SOD7 and competed with it for binding to the jasmonate transcription factors MYC2/4, and that SOD7 and MYC2/4 worked together to strongly repress KLU expression, restricting seed size.

In addition, researchers showed that the JA-SOD7-KLU regulatory mechanism played a critical role under salt stress, highlighting its importance in environmental adaptation. They also showed that SOD7 interacted with the germination regulator ABI5, suggesting that it may coordinate seed development and germination.

"Our work unveils a sophisticated molecular circuit where jasmonate signaling, through key interactions between JAZ, MYC, SOD7, and KLU, fine-tunes seed size," said HU Yanru from XTBG. "Understanding these mechanisms is vital for deciphering how plants balance growth with environmental adaptation, and offers potential strategies for improving crop traits."