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Abscisic acid (ABA), a key environmental response hormone, strongly inhibits seed germination and serves as a central regulator in this process. While significant progress has been made in deciphering the molecular mechanisms of ABA-mediated germination suppression, the potential specificity of ABA signaling and seed germination regulation under specific environmental conditions remains unclear.

In a study in The Plant Cell, researchers from the Xishuangbanna Tropical Botanical Garden of the Chinese Academy of Sciences (CAS), the University of Science and Technology of China of CAS, and Hunan University, revealed how nitrate counteracts ABA-mediated suppression of seed germination in Arabidopsis (Arabidopsis thaliana), and discovered an antagonistic relationship between nitrate signaling and ABA pathways mediated through key transcriptional regulators.

Researchers investigated the mechanism by which nitrate promoted seed germination through Nin-Like Protein 8 (NLP 8) through gene expression analysis and biochemical experiments. They analyzed the expression of the NLP8 gene in Arabidopsis seeds cultured under different nitrate concentrations and examined the expression levels of downstream genes related to ABA signaling. They also observed the effects of different treatments on seed germination rates and germination times.

The results showed that when potassium nitrate and ABA were applied exogenously, nitrate partially alleviated ABA-induced seed germination delay. The nitrate signaling hub NLP8 physically interacted with and suppressed the activity of ABA pathway regulators ABI3 and ABI5. The nitrogen compound mitigated ABA responses during germination without altering ABA levels.

Notably, NLP8 overexpression was shown to suppress ABA hypersensitivity in mutants with impaired nitric oxide pathways, suggesting potential applications for improving seed vigor under stress conditions.

"Our study reveals that NLP8-ABI3/ABI5 module serves as a molecular fulcrum balancing environmental nutrient availability with developmental restraint mechanisms. It provides insights for developing strategies to enhance crop establishment in suboptimal environments," said Prof. Hu Yanru, the corresponding author of this study.