Genome-Wide Identification and Temporal Expression Profiling of the GDSL Esterase/Lipase Family Following Meloidogyne incognita Inoculation in Watermelon (Citrullus lanatus)

GDSL esterase/lipase (GELP) proteins are involved in lipid metabolism, cell wall modification, and plant immune regulation; however, their genome-wide characterization and potential roles in watermelon responses to Meloidogyne incognita infection remain largely unexplored. Through genome-wide analysis, 75 ClGELP family members were identified in watermelon ‘97103’, and their expansion was primarily driven by whole-genome duplication and segmental duplication events. All GELP proteins contained the GDSL domain. They exhibited substantial divergence in molecular weight, isoelectric point, and subcellular localization. Cis-regulatory element analysis of the promoters revealed that ClGELP genes contain hormone-responsive elements and stress- and defense-associated cis-elements. Transcriptome profiling at 0, 5, 10, 15, 20, and 25 days post-inoculation (dpi), with each post-inoculation time point compared with 0 dpi as the baseline reference, revealed that 28 members showed significant temporal changes after inoculation relative to 0 dpi. Among these genes, ClGELP72 exhibited the highest induction level, reaching a maximum expression increase of 4.40-fold at 20 days post-inoculation (dpi) compared to 0 dpi. In contrast, the expression levels of ClGELP11 and ClGELP74 decreased 3.03-fold at 25 dpi and 2.90-fold at 20 dpi, respectively, relative to 0 dpi. Collectively, ClGELP72, ClGELP11, and ClGELP74 represent promising candidates for future functional studies aimed at elucidating their potential roles in watermelon responses to M. incognita infection.