Transcriptome analysis revealed the potential molecular mechanism of style bending movement in passion fruit...

Passion fruit has a difficult natural fruiting process and low yield due to its approach herkogamy. Understanding the molecular mechanism of passion fruit style bending is crucial as it enhances pollination efficiency by optimizing stigma-anther alignment, overcoming herkogamy and improving fruit yield. In this study, we used the purple passion fruit variety 'Tainong 1' as experimental material. We observed that its style bends into an "S"-shape after flowering. As development progresses, the degree of this S-shaped curvature gradually weakens. Simultaneously, the style also exhibits a spatial bending from top to bottom during this process. In order to identify the genes specifically induced during the style bending process, transcriptome analysis was conducted on styles at T₁ (flowering), T₂ (30 min post-flowering), and T₅ (120 min post-flowering). 226 DEGs were identified to be specifically expressed in the T₁ to T₂ stages, mainly enriched in the "Protein processing in endoplasmic reticulum" pathway, involving heat shock proteins and DnaJ family proteins, suggesting that heat stress response is involved in early style movement regulation. The enriched 18 DEGs were all heat shock protein family proteins and DnaJ family proteins, which may be due to the stress response of the style to environmental heat stimulation. At the same time, 1,080 DEGs were specifically expressed in the T₂ to T₅ stages, mainly enriched in the "Phenylpropanoid biosynthesis" pathway and involved in the lignin biosynthesis pathway. Physiological testing confirmed that as the S-shaped of the style weakens, lignin accumulates significantly, increasing by 60% from T₁ to T₂ and by 43% from T₂ to T₅, which is consistent with the trend of transcriptome data. In addition, differential expression of hormone metabolism related genes (abscisic acid, brassino steroids, jasmonic acid, and gibberellin pathways) was observed. Endogenous hormone quantification further confirmed hormonal regulation of style bending, revealing distinct accumulation patterns: ABA showed a biphasic trend with an initial 30% increase (T₁ to T₂) followed by a 9% rise (T₂ to T₅), while jasmonic acid exhibited a sharper 30% (T₁ to T₂) to 22% (T₂ to T₅) escalation. In summary, our results indicate that lignin accumulation enhances the mechanical strength of the style and reduces its inherent S-shaped bending. Thermal stimulation and hormone synthesis metabolism may also play a role in the process of style bending, but further research is needed to determine the specific mechanisms by which the response is regulated.