Genome-wide Identification of the CsnsLTP Gene Family in Cucumber and Expression Profiling in Response to Corynespora cassiicola

Abstract

Aims: This study aims to characterise the molecular properties and structural features of the non-specific lipid transfer protein (CsnsLTP) gene family and to analyse its expression patterns in cucumber. Candidate CsnsLTP genes that may contribute to resistance to Corynespora cassiicola infection will be identified and may provide valuable genetic resources for molecular breeding against cucumber target leaf spot disease. Study Design: The resistant cultivar Jinyou 38 and the susceptible cultivar Xintaimici were used as plant materials. Seedlings at the two-leaf and one-bud stage were inoculated with C. cassiicola. Samples were collected at eight time points spanning 0–144 h post-inoculation. CsnsLTP family members were identified through a combination of bioinformatic and expression analyses, and their infection-responsive characteristics were subsequently characterised. Methodology: Thirteen CsnsLTP genes were retrieved from the NCBI database. Multiple bioinformatic tools, including ExPASy, CELLO, MEGA, MEME, NCBI Batch CD-Search, and TBtools, were used to systematically characterise the deduced proteins, including their physicochemical properties, subcellular localisation, phylogenetic relationships, chromosomal distribution, conserved motifs, conserved domains, and exon–intron gene structures. Reverse transcription quantitative PCR (RT-qPCR) was then used to quantify the relative transcript abundance of all target genes in resistant and susceptible cucumber cultivars at distinct time points after C. cassiicola inoculation. Results: The 13 CsnsLTP genes were unevenly distributed across chromosomes 1, 3, 4, 5, and 7 and exhibited significant variation in their physicochemical properties. Subcellular localisation predictions indicated that most encoded proteins were localised to the plasma membrane, although some were also predicted to reside in the cell wall, chloroplasts, and other compartments. Phylogenetic analysis classified the family members into three subfamilies, with Motif 1 identified as a conserved motif shared by subfamilies II and III. Expression profiling revealed that CsnsLTP1, CsnsLTP4, CsnsLTP5, CsnsLTP7, CsnsLTP8, CsnsLTP9, CsnsLTP10, CsnsLTP12, and CsnsLTP13 were significantly differentially expressed between resistant and susceptible cultivars following C. cassiicola infection, suggesting that they are candidate genes associated with resistance to target leaf spot in cucumber. Conclusions: This study identified 13 CsnsLTPs in cucumber and systematically characterised their molecular and structural features. Pathogen-induced expression screening identified nine candidate resistance-associated genes. These findings provide candidate genes and a theoretical basis for the molecular genetic improvement of target leaf spot resistance in cucumber.