The Arabidopsis NLP7-HB52/54-VAR2 pathway modulates energy utilization in diverse light and nitrogen conditions

In plants, nitrate is the dominant nitrogen (N) source and a critical nutrient signal regulating various phy-siological and developmental processes.1-4 Nitrate-responsive gene regulatory networks are widely believed to control growth, development, and life cycle in addition to N acquisition and utilization,1-4 and NIN-LIKE PROTEIN (NLP) transcriptional activators have been identified as the master regulators governing the net-works.5-7 However, it remains to be elucidated how nitrate signaling regulates respective physiological and developmental processes. Here, we have identified a new nitrate-activated transcriptional cascade involved in chloroplast development and the maintenance of chloroplast function in Arabidopsis. This cascade consisting of NLP7 and two homeodomain-leucine zipper (HD-Zip) class I transcription factors, HOMEOBOX PROTEIN52 (HB52) and HB54,8,9 was responsible for nitrate-and light-dependent expression of VAR2 encoding the FtsH2 subunit of the chloroplast FtsH protease involved in the quality control of photo -damaged thylakoid membrane proteins.10,11 Consistently, the nitrate-activated NLP7-HB52/54-VAR2 pathway underpinned photosynthetic light energy utilization, especially in high light environments. Further-more, genetically enhancing the NLP7-HB52/54-VAR2 pathway resulted in improved light energy utilization under high light and low N conditions, a superior agronomic trait. These findings shed light on a new role of nitrate signaling and a novel mechanism for integrating information on N nutrient and light environments, providing a hint for enhancing the light energy utilization of plants in low N environments.

Automated summary

In this study, a new nitrate-activated transcriptional cascade involved in chloroplast development and function maintenance was identified. This cascade regulates the expression of VAR2 gene, which is responsible for quality control of photo-damaged thylakoid membrane proteins. The cascade also plays a role in enhancing photosynthetic light energy utilization, especially in high light environments. These findings provide insights into a novel mechanism for integrating information on nitrogen and light environments, and have implications for improving light energy utilization in plants under low nitrogen conditions.