Exploring Morphological, Transcriptomic, and Metabolomic Differences Between Two Sister Lines with Contrasting Resistance to Orange Rust Disease in Sugarcane

Sugarcane (<i>Saccharum</i> spp.) hybrid, one of the most important crops in Florida, has been affected by orange rust (OR) disease caused by <i>Puccinia kuehnii</i> since 2007, resulting in significant yield loss. Developing resistant cultivars to this disease has become an important goal in sugarcane breeding programs. However, the specific genes and molecular mechanisms underlying the resistance to OR disease in sugarcane are still not clear. In this study, we selected two sugarcane sister lines with different genotypes-showing contrasting resistance responses to the disease-from a major quantitative trait loci (QTL) region controlling OR disease resistance. Morphological and anatomical observations revealed that the resistant line (540) had significantly smaller stomatal size and lower stomatal density than the susceptible line (664). Transcriptomic analyses showed that resistant line 540 had increased cell surface modification activity, suggesting possible increased surface receptors. Differentially expressed gene and coexpression analyses also revealed key genes involved in the biosynthesis of anti-fungal molecules, such as hordatines, arabidopyrones, and alkaloids. They also showed a strong increase in long non-coding RNA expression, playing a role in transcriptional regulation. Transcriptomic-metabolomic joint analysis suggested that the biosynthesis of phenylpropanoid derivatives with purported antioxidant and anti-fungal capabilities increased in line 540, especially those deriving from ferulate. Genes, pathways, and some single-nucleotide polymorphisms identified in this study will provide fundamental information and resources to advance the knowledge of sugarcane molecular genetic mechanisms in relation to OR disease, supporting breeding programs in developing cultivars with improved resistance to OR.