ZmMYB37 and ZmMYB77 act together to enhance stalk strength by promoting secondary wall deposition in maize

Lodging is a major factor limiting maize yield potential and production stability. Stalk lodging, the predominant form, is largely determined by stalk strength, which depends on stalk morphology and secondary cell wall (SCW) deposition. However, the regulatory mechanisms underlying these traits remain poorly understood. Here, we identified two homologous R2R3-MYB transcription factors, ZmMYB37 and ZmMYB77, as positive regulators of SCW deposition and stalk strength in maize. Both genes were preferentially expressed in stalk tissues, and loss-of-function mutants exhibited softer and more fragile stalks with significantly reduced bending strength and rind penetrometer resistance. Microscopic analyses further revealed that single and double mutants displayed reduced vascular bundle area, thinner vascular bundle sheaths, decreased vascular bundle sheath cell wall thickness in the peripheral layer, and thinner sclerenchymatous hypodermis. Consistently, the accumulation of SCW components, including lignin, cellulose, and hemicellulose, was markedly reduced in mutant stalks. Transcriptome and RT-qPCR analyses revealed the downregulation of SCW biosynthesis genes and upregulation of SCW metabolism genes in the Zmmyb37/77 double mutants relative to wild type plants. Cis-acting element analysis and dual-luciferase reporter assays further showed that ZmMYB37 and ZmMYB77 activate the expression of a set of SCW-related genes. Collectively, our findings demonstrate that ZmMYB37 and ZmMYB77 function as positive regulators linking SCW deposition with stalk strength, highlighting their potential as genetic targets for improving lodging resistance in maize.