Draft Genome Assembly and Differential Expression of MpPPO1 and MpPPO2 Across Green-Fruit Development in Ecuadorian Musa paradisiaca L.

Abstract

Ecuador ranks among the world’s leading banana exporters; however, postharvest enzymatic browning, driven by polyphenol oxidases (PPOs), remains an important determinant of fruit quality loss and reduced market value. The genes encoding PPOs in Musa paradisiaca L., a triploid hybrid (AAB) widely cultivated in Ecuador, have not previously been described at the genomic or transcriptional level. The objective of this study was to generate a preliminary de novo draft assembly of Ecuadorian M. paradisiaca, identify PPO-coding loci recovered in this assembly, and compare their relative expression across three field-defined green-fruit developmental stages: early, intermediate, and physiologically mature-green. High-molecular-weight genomic DNA sequencing was performed using the Oxford Nanopore MinION Mk1B platform, and 13,239 contigs were obtained by de novo assembly with Flye v2.9.6. Two intronless PPO-coding loci, designated MpPPO1 and MpPPO2, were identified and deposited in GenBank under accessions PX565008 and PX565009. qRT-PCR showed significantly higher MpPPO1 expression at the physiologically mature-green stage, whereas MpPPO2 showed only a non-significant trend toward higher expression at the intermediate stage. These profiles indicate transcriptional divergence and identify MpPPO1 as a candidate associated with late green-fruit development or physiological maturity. However, because stage classification relied on a qualitative field harvest index and neither controlled postharvest ripening nor quantitative maturity, PPO activity, or browning measurements were performed, the results do not demonstrate ripening-induced activation, functional subfunctionalization, or causality in browning. These findings provide a preliminary molecular basis for future functional and postharvest studies in commercial banana cultivars.