Transcriptome analysis provides insights into aril development regulated gene network in lychee, longan, and rambutan

Lychee (Litchi chinensis Sonn.), longan (Dimocarpus longan Lour.), and rambutan (Nephelium lappaceum L.) are popular tropical fruits in the family Sapindaceae, known for their succulent arils-specialized seed appendage with significant biological and commercial value. Despite their agricultural relevance, the molecular mechanisms underlying aril development in these species remain poorly understood.

We conducted RNA-sequencing to profile transcriptomes during aril development, complemented by in-situ hybridization to validate the spatial expression of LcLBD1. OrthoFinder identified species-specific and shared differentially expressed genes (DEGs), while functional enrichment analyses (GO, KEGG) and transcriptional network modeling elucidated regulatory pathways. After detailed analyses of transcriptomes, species-specific and shared DEGs were identified across lychee, longan, and rambutan using OrthoFinder. Members of the bHLH and MYB gene families were implicated in early aril development. Species-specific DEGs were primarily enriched in metabolic pathways. From shared DEGs, we identified ten transcription factors (AGL8, AP3, SHP1, WOX13, LBD1, LBD3, OBP1, SPL2, SPL3, and SPL9) and three genes (IAA8, CSLD5, and CYCD3;2) as key regulators. Interestingly, in-situ hybridization localized LcLBD1 expression to funicle and small aril cells, suggesting roles in cell differentiation and division.

We have identified ten transcription factors and three genes affecting aril development in lychee, longan, and rambutan, and validated the expression of LcLBD1 in funicle and aril cells. These results offer a new perspective on the molecular mechanism of aril development and lay the groundwork for future research into the functions and regulatory mechanisms of candidate genes.