# GmNMHC5 Modulates Gibberellin Homeostasis to Balance Carbon–Nitrogen Metabolism and Enhance Protein Yield in Soybean

## TL;DR

Knocking out the GmNMHC5 gene in soybean increases protein yield by boosting gibberellin levels and improving carbon-nitrogen balance.

## Contribution

This study identifies GmNMHC5 as a key regulator of gibberellin homeostasis affecting soybean protein yield through carbon–nitrogen metabolism.

## Key findings

- GmNMHC5 knockout increases gibberellin biosynthesis, plant height, and seed protein accumulation.
- Overexpression of GmNMHC5 reduces gibberellin levels, plant growth, and protein yield.
- Modulating GmNMHC5 provides a strategy to enhance soybean protein yield without affecting total seed yield.

## Abstract

Soybean, a vital source of high‐quality plant‐based protein and oil, continues to be a focal crop for improving yield and quality. Gibberellins (GAs), as key regulators of plant growth and development, hold significant potential for enhancing these traits in soybean. In this study, previously developed GmNMHC5 mutant lines were utilized to assess GA levels, photosynthetic capacity, carbohydrate and nitrogen accumulation, as well as yield and quality characteristics during the seed‐filling stage. Knockout of GmNMHC5 was found to enhance endogenous GA biosynthesis, resulting in increased plant height and improved carbon and nitrogen metabolism. These physiological changes contributed to significant increases in both seed weight and size, leading to higher accumulation of carbohydrate and protein reserves in mature seeds. Although total seed yield remained unchanged, protein yield per plant was significantly elevated in the GmNMHC5 knockout line. In contrast, overexpression of GmNMHC5 led to reduced GA levels, decreased plant height, and diminished aboveground dry matter accumulation, ultimately lowering protein yield. These findings indicate that targeted knockout of GmNMHC5 can enhance protein yield in soybean by modulating GA levels and optimizing carbon–nitrogen allocation. This study provides a theoretical basis and valuable genetic resources for the development of high‐protein soybean cultivars.

The GmNMHC5 knockout elevated gibberellin (GA) biosynthesis, resulting in increased plant height and greater accumulation of carbohydrates and proteins in mature seeds, thereby enhancing protein yield per plant without altering total yield. Conversely, GmNMHC5 overexpression lines exhibited reduced GA levels, suppressed plant growth, and decreased aboveground dry matter accumulation, ultimately resulting in lower protein yield. These results suggest that GmNMHC5 knockout enhances soybean protein yield by fine‐tuning GA homeostasis and optimizing carbon–nitrogen allocation.