A Large Transposon Insertion in the <i>stiff1</i> Promoter Increases Stalk Strength in Maize

Abstract

Stalk lodging, which is generally determined by stalk strength, results in considerable yield loss and has become a primary threat to maize (<i>Zea mays</i>) yield under high-density planting. However, the molecular genetic basis of maize stalk strength remains unclear, and improvement methods remain inefficient. Here, we combined map-based cloning and association mapping and identified the gene <i>stiff1</i> underlying a major quantitative trait locus for stalk strength in maize. A 27.2-kb transposable element insertion was present in the promoter of the <i>stiff1</i> gene, which encodes an F-box domain protein. This transposable element insertion repressed the transcription of <i>stiff1</i>, leading to the increased cellulose and lignin contents in the cell wall and consequently greater stalk strength. Furthermore, a precisely edited allele of <i>stiff1</i> generated through the CRISPR/Cas9 system resulted in plants with a stronger stalk than the unedited control. Nucleotide diversity analysis revealed that the promoter of <i>stiff1</i> was under strong selection in the maize stiff-stalk group. Our cloning of <i>stiff1</i> reveals a case in which a transposable element played an important role in maize improvement. The identification of <i>stiff1</i> and our edited <i>stiff1</i> allele pave the way for efficient improvement of maize stalk strength.