Expression and Functional Analysis of PeFT Genes in Flowering Regulation of Passion Fruit

Background/Objectives: Passion fruit (Passiflora edulis Sims) is an economically important tropical vine fruit crop. Frequent high-temperature stress disturbs normal floral bud differentiation and causes defective flowering, which imposes severe constraints on its yield and quality. To date, the key genes regulating flowering in passion fruit remain poorly understood. FLOWERING LOCUS T (FT) functions as the core florigen that integrates environmental and endogenous signals to govern the flowering in plants. Methods: In this study, two FT homologs, designated PeFT1 and PeFT2, were identified and cloned from passion fruit cultivar ‘Tainong No. 1’. Bioinformatics analysis of these two genes was systematically performed, and their spatiotemporal expression profiling, temperature stress response, and subcellular localization were analyzed. Heterologous overexpression in Arabidopsis thaliana was also conducted to dissect the functions. Results: Both PeFT1 and PeFT2 belong to the FT-like subfamily of the PEBP family, harboring a complete conserved PEBP domain, and were localized to the nucleus. PeFT2 transcripts were highly abundant in leaves and reached peak expression at the rapid growth stage, exhibiting dynamic changes consistent with the continuous flowering habit of passion fruit, whereas PeFT1 was predominantly expressed in mature stem tissues and exhibited the highest expression level in open flowers. Under different temperature treatments, the expression of PeFT2 was markedly promoted at 33 °C but repressed at 38 °C, while PeFT1 showed decreased expression at 28 °C and was transiently activated by treatment at 33 °C. Heterologous overexpression of PeFT2 in A. thaliana significantly promoted early flowering and markedly upregulated the expression of endogenous flowering genes AtFT, AtSVP and AtSOC1. Conclusions: These results suggest that PeFT1 and PeFT2 have functional divergence. PeFT2 may play a role in flowering regulation in passion fruit and function as a positive regulator. Our findings provide new insight into the molecular mechanism of flowering regulation in passion fruit.