In a study published in Nature on June 3, research teams led by WU Yongrui and WANG Haihai from the Center for Excellence in Molecular Plant Sciences of the Chinese Academy of Sciences, along with WANG Wenqin's team from Shanghai Normal University and Yongcai Huang's team from Sichuan Agricultural University, have successfully cloned Teosinte high protein 3 (THP3-T), a key gene from maize's wild ancestor, teosinte, which significantly enhances seed protein content.

Maize (Zea mays L.) plays an important role in global food security. However, modern maize varieties often suffer from low seed protein content, leading to a heavy reliance on imported soybean meal for livestock feed. During the 9,000-year history of maize domestication and modern breeding, the lack of directional selection for protein content resulted in the "loss" of many beneficial alleles.

In this study, the researchers found that THP3-T encodes glutamate-oxaloacetate transaminase 1 (GOT1), a central enzyme in the nitrogen assimilation pathway. They showed that natural variations in the promoter and coding sequence of THP3-T boost both its expression and enzymatic activity, optimizing nitrogen partitioning toward protein synthesis. Notably, THP3-T was inadvertently disfavored during domestication, with its frequency in modern maize lines dropping to only 2.1%.

Furthermore, the researchers demonstrated a powerful synergistic effect when THP3-T is pyramided with THP9-T which encodes asparagine synthase 4. By introgressing both superior alleles into Zhengdan958, a widely cultivated elite maize hybrid in China, they achieved a significant increase in seed protein content from 8.5% to 12-13%, and in whole-plant protein content from 7% to over 9%, all without compromising grain yield.

This study reveals the molecular mechanism behind the decline in maize protein content during domestication. By reintroducing the beneficial rare alleles from wild relatives, it provides a powerful genetic tool for breeding high-protein maize varieties, offering a promising way to address the issue of global food and feed demands. The study marks another breakthrough after the identification of the first high-protein gene, THP9-T.