Identification and characterization of four novel xiaomi alleles to facilitate foxtail millet as a C₄ model plant

A diverse genetic background is essential for genetic analysis and functional genomics research in model plants. In this study, four novel xiaomi-like mutants in different genetic backgrounds, named xiaomi3, xiaomi4, xiaomi5, and xiaomi6, were identified and characterized. These mutants exhibited an extremely early heading phenotype, with heading occurring around 30–40 days after sowing under natural long-day conditions. Significant reductions in plant height, leaf length, leaf width, panicle length, and panicle diameter were observed in the mutants compared to their corresponding wild-types. Notably, these mutants displayed diverse panicle architectures and hull colors, effectively preventing seed mixing between them. Subsequent investigation under controlled short-day and long-day conditions confirmed the significant early heading phenotype of these mutants. Molecular characterization revealed that mutations in the Phytochrome C (SiPHYC) gene, including transposon insertions and a frame shift mutation, were responsible for the extremely early heading phenotype. RNA-sequencing (RNA-Seq) analysis identified 19 differentially expressed genes associated with this phenotype. Additionally, genome-wide InDels and SNPs were identified, providing valuable resources for marker-assisted breeding and genetic studies. These findings will contribute to our understanding of the genetic and molecular mechanisms underlying SiPHYC-mediated photoperiod flowering, and provide valuable resources that will push xiaomi as a C₄ model plant.