China Agricultural University researchers discover key gene regulating cuticular wax and drought tolerance in sorghum

As global climate change intensifies and agricultural environments become increasingly arid, understanding the adaptive mechanisms of terrestrial plants is critical for global food security. Plant cuticular wax forms a vital hydrophobic barrier that protects crops from severe water loss, UV radiation, and pathogen infection. Sorghum (Sorghum bicolor (L.) Moench), a major drought-tolerant crop, is valued for its thick cuticular wax layer, which markedly enhances resilience to abiotic stresses. However, the key regulatory mechanisms governing cuticular wax accumulation and very-long-chain fatty acid (VLCFA) biosynthesis have remained largely uncharacterized.

To address these gaps, a research team led by Prof. Hongwei Cai and Assoc. Prof. Jun Chen from China Agricultural University identified a novel bloomless mutant, bm-sz, and cloned its causal gene, BM-SZ, revealing a new regulatory network underlying sorghum wax biosynthesis. The study was published online in The Crop Journal.

"Using ethyl methane sulfonate (EMS) mutagenesis, we isolated the bm-sz mutant, which showed an approximately 80% reduction in total wax content and severe drought sensitivity," explained first author Candong Xiong. "Through map-based cloning and MutMap analysis, we confirmed that BM-SZ, which encodes a putative α/β hydrolase, is the causal gene for the bloomless phenotype."

The main findings are as follows:

• Phenotypic and lipidomic profiling: Quantitative lipidomics showed that the bm-sz mutant had significantly reduced levels of VLCFAs (especially those with chain lengths exceeding C20), primary alcohols, and other wax components, resulting in higher cuticle permeability and faster water loss under drought stress.
• Structural and functional insights: AlphaFold3 structural modeling indicated that the G198R mutation may disrupt the central hydrophobic catalytic pocket of the BM-SZ protein. This structural impairment likely abolishes ligand-binding or enzymatic activity, making the enzyme nonfunctional even in the absence of a premature stop codon.
• Transcriptomic regulatory mechanism: RNA-seq analysis revealed that the BM-SZ protein positively regulates wax and VLCFA biosynthesis by modulating the expression of key downstream wax biosynthetic genes, especially those in the 3-KETOACYL-COA SYNTHASE (KCS) family.

Furthermore, the team performed haplotype analysis using 659 sorghum accessions. "We found that BM-SZ is highly conserved across sorghum germplasm, with no natural loss-of-function variants detected in the examined population, highlighting its essential and irreplaceable role in epicuticular wax formation during sorghum evolution," says Cai.

The structural and transcriptomic analyses suggest that BM-SZ may have dual functions: acting not only as a metabolic enzyme but also potentially as a signaling receptor. "Mutations in the catalytic pocket likely disrupt a key signaling cascade, leading to the transcriptional repression of the entire wax biosynthetic pathway," adds Cai.

This discovery clarifies the functions and regulatory modes of the α/β hydrolase family in sorghum, providing a valuable genetic target and theoretical basis for molecular breeding of high-drought-tolerance crops.

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Contact the author: Hongwei Cai (caihw@cau.edu.cn) & Jun Chen (chenj@cau.edu.cn)

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