Analysis of non-specific lipid transfer proteins in sorghum revealed specific clades involved in the formation of protective barriers in pollen, seed, and root tissues

Non-specific lipid transfer proteins (nsLTPs) are small, cysteine-rich proteins involved in non-vesicular lipid transport, which is essential for cuticle and wax deposition, pollen exine formation, pollen tube guidance, seed maturation, and stress adaptation. Since their status as a large gene family allows for functional redundancy and specialization, an analysis combining structure, phylogeny, and expression is crucial to decipher their roles in sorghum, a globally prominent cereal crop. In this study, we identified 77 nsLTPs from sorghum and classified them into six distinct classes (Types 1, 2, C, D, G, and X). The type 2 and type X genes exhibit pronounced tandem duplication-driven amplification, whereas the type G class appears to have expanded primarily through whole-genome/segmental duplications. Comparative phylogenetic analysis with Arabidopsis , rice, and maize revealed clear evolutionary divergence between dicot and monocot-specific clades, with sorghum nsLTPs clustering closely with maize homologs, consistent with their shared lineage. Notably, type C nsLTPs formed conserved clades associated with the anther development, a pattern further supported by expression analyses and published literature for orthologous genes. Type X genes, on the other hand, were predominantly detected in root tissues. By combining empirical data on orthologous genes from the literature with expression analysis, type G genes were identified as being implicated in lipid barrier formation in pollen, seed, and root tissues, as well as in response to drought stress. The data presented here are pivotal to prioritizing LTP genes for functional validation and deciphering the evolutionary adaptation in sorghum.