Integrative Bioinformatic, Transcriptional, and Enzymatic Analysis Reveals Differential Regulation of Rhamnogalacturonan Lyase During Postharvest Ripening of Soursop (Annona muricata L.) Varieties

Soursop fruit (Annona muricata L.) exhibits a rapid loss of firmness during postharvest ripening, mainly attributed to pectin depolymerization and cell wall restructuring. Among the enzymes involved, rhamnogalacturonan lyase (RGL), belonging to the PF06045 protein family, contributes to the degradation of rhamnogalacturonan I (RG-I), a key structural component of pectin. However, the regulatory mechanisms and transcriptional dynamics of RGL genes in tropical fruits remain poorly characterized. This study aimed to evaluate RGL in three soursop varieties (GUANAY-1, GUANAY-2, and GUANAY-3) during postharvest ripening through integrative bioinformatic, transcriptional, and enzymatic analyses. Bioinformatic analysis identified five soursop genes containing the PF06045 domain, designated RGL1–RGL5, which were grouped into three phylogenetic clusters. Differential expression analysis revealed that RGL1, RGL2, and RGL3 were differentially expressed, while functional enrichment analysis indicated that these genes are mainly associated with lyase activity and cell wall polysaccharide disassembly. Quantitative polymerase chain reaction (qPCR) revealed variety-dependent transcriptional patterns. RGL2 showed expression peaks on day 5 in GUANAY-1 and GUANAY-3 and on day 7 in GUANAY-2, while RGL3 reached its maximum expression on day 5 in all varieties. Enzymatic activity also varied among varieties, showing concordance with RGL2 and RGL3 expression in GUANAY-1, a delayed maximum in GUANAY-2, and a progressive decline in GUANAY-3. Principal component analysis explained 87.2% of the total variation, with enzymatic activity contributing mainly to PC1 and RGL2 and RGL3 expression to PC2. Overall, these results demonstrate differential regulation of RGL among soursop varieties and confirm its central role in RG-I degradation during postharvest fruit softening.