Corn Got Better at Turning Growth Into Grain
A corn plant can add biomass without adding much grain. Plant breeders measure the difference with harvest index: grain weight divided by the plant’s total biomass.
The researchers compared wild teosinte, pre-Columbian landraces, and modern inbred maize. Harvest index measured 0.26 in teosinte, 0.42 in landraces, and 0.52 in modern inbred lines.
Harvest index is the share of a plant’s total biomass that ends up in harvested grain.
Values reported in the paper
That history gave the team a place to look for the genes that changed how maize distributes carbon and nitrogen. They mapped 20 regions associated with harvest index in two populations derived from crosses between maize and teosinte. One region appeared in both.
A 9,100-Base Insertion Survived Domestication
The shared region contained HI1, a noncoding DNA sequence about 9,100 bases long. The researchers found it in 56.4 percent of the wild teosinte population they examined, 99.4 percent of pre-Columbian landraces, and every modern maize line in the study.
HI1 is an enhancer, a stretch of DNA that controls another gene. Its target, BRR1, sits roughly 22,000 bases away along the chromosome. Inside the nucleus, the chromosome folds until the two regions can make contact.
The Chromosome Brings HI1 and BRR1 Together
The protein CONZ1 binds HI1 and the BRR1 promoter. It recruits GCN5, an enzyme that changes how tightly the local DNA is packed. The experiments linked those proteins to a chromatin loop between the enhancer and the gene.
BRR1 then activates genes involved in sugar transport, nitrogen assimilation, and amino-acid movement. It also activates the flowering signals ZCN8 and ZCN12. The same regulatory chain helps begin reproduction and supply the developing ear.
Breaking BRR1 Changed the Whole Plant
Knocking out BRR1 reduced harvest index, total biomass, and grain yield. Increasing its expression raised all three. BRR1-deficient plants retained more carbon, nitrogen, and dry matter in leaves and stems, while plants with higher BRR1 activity moved more of those materials into the ear.
This is source-to-sink allocation. Leaves produce sugars and release stored nutrients. Developing kernels receive them. BRR1 changes the expression of the transport and metabolism genes that connect those parts of the plant.
The Field Trials Produced More Grain
The team tested plants with higher BRR1 expression in Tieling, Sanya, and Beijing. Grain yield increased by 10 to 16 percent under normal conditions across the three locations.
Under low-nitrogen conditions, the BRR1-enhanced plants produced 28 percent more grain than the comparison plants. The authors also report that the added yield preserved grain protein and mechanical stalk strength.
BRR1 Gives Breeders a Specific Control Point
Modern maize already carries HI1. The breeding target now sits downstream at BRR1, where changes in gene expression can alter flowering, nutrient movement, biomass, and grain yield together.
A crop can capture plenty of sunlight and still send too little of its accumulated carbon and nitrogen into grain. HI1 and BRR1 give breeders a specific control point for that transfer.