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Abiotic stress is the focus of passion fruit research since it harms the industry, in which high temperature is an important influencing factor. Dof transcription factors (TFs) act as essential regulators in stress conditions. TFs can protect against abiotic stress via a variety of biological processes. There is yet to be published a systematic study of the Dof (PeDof) family of passion fruit. This study discovered 13 PeDof family members by using high-quality genomes, and the members of this characterization were identified by bioinformatics. Transcriptome sequencing and qRT-PCR were used to analyze the induced expression of PeDofs under high-temperature stress during three periods, in which PeDof-11 was significantly induced with high expression. PeDof-11 was then chosen and converted into yeast, tobacco, and Arabidopsis, with the findings demonstrating that PeDof-11 could significantly respond to high-temperature stress. This research lays the groundwork for a better understanding of PeDof gene regulation under high-temperature stress.

Aroma is an important factor in fruit quality. Passiflora edulis (passion fruit) is popular among consumers because of its rich flavor and nutritional value. Esters are the main components of the volatile aroma of passion fruit. Lipoxygenase (LOX), as the first key enzyme upstream of esters, may play an important role in the formation of passion fruit aroma. In this study, a total of 12 passion fruit LOX (PeLOX) members were screened out based on the Passiflora edulis genome database, which were distributed unevenly on 6 chromosomes, all containing the highly conserved lipoxygenase domain and some containing the PLAT domain. The gene structure, evolutionary analysis and cis-acting elements of the family members were predicted in this study. Transcriptome analysis showed that 12 PeLOX genes had different degrees of response to different abiotic stresses (drought stress, salt stress, cold stress, and high temperature). PeLOX1, PeLOX2, PeLOX7, PeLOX11, and PeLOX12 responded significantly to various abiotic stresses, while PeLOX8 and PeLOX9 had little change in expression in all stresses. Quantitative real-time PCR (qRT-PCR) in six tissues revealed that the 12 PeLOX genes exhibited tissue expression specificity, and the relative expression of most genes were particularly high in the roots, stems, and fruits. Focusing on passion fruit ripening and ester synthesis, the transcriptomic analysis showed that with the increase in fruit development and fruit maturity, the expression levels of PeLOX1, PeLOX9, PeLOX11, and PeLOX12 showed downregulated expression, while PeLOX2 and PeLOX4 showed upregulated expression. In particular, the upregulation trend of PeLOX4 was the most obvious, and the qRT-PCR results were consistent with the transcriptome result. Pearson correlation analysis showed that with the development and ripening of fruit, the expression level of PeLOX4, LOX enzyme activity and total ester content all showed an increasing trend, in particular during the period when the peel was red and shrank (from T2 to T3 stage), the esters’ contents increased by 37.4 times; the highest expression levels were all in the T3 period. The results indicated that PeLOX4 may be a candidate gene involved in fruit ripeness and the formation of volatile aroma compounds, with the increase in fruit ripening, the expression level of PeLOX4 increased and the LOX enzyme activity increased accordingly, thereby promoting the synthesis of volatile esters in fruit pulp. Our discovery lays the foundation for the functional study of LOX in passion fruit.

Aquaporins (AQPs) in plants can transport water and small molecules, and they play an important role in plant development and abiotic stress response. However, to date, a comprehensive study on AQP family members is lacking. In this study, 27 AQP genes were identified from the passion fruit genome and classified into four groups (NIP, PIP, TIP, SIP) on the basis of their phylogenetic relationships. The prediction of protein interactions indicated that the AQPs of passion fruit were mainly associated with AQP family members and boron protein family genes. Promoter cis-acting elements showed that most PeAQPs contain light response elements, hormone response elements, and abiotic stress response elements. According to collinear analysis, passion fruit is more closely related to Arabidopsis than rice. Furthermore, three different fruit ripening stages and different tissues were analyzed on the basis of the transcriptome sequencing results for passion fruit AQPs under drought, high-salt, cold and high-temperature stress, and the results were confirmed by qRT-PCR. The results showed that the PeAQPs were able to respond to different abiotic stresses, and some members could be induced by and expressed in response to multiple abiotic stresses at the same time. Among the three different fruit ripening stages, 15 AQPs had the highest expression levels in the first stage. AQPs are expressed in all tissues of the passion fruit. One of the passion fruit aquaporin genes, PeTIP3-2, which was induced by drought stress, was selected and transformed into Arabidopsis. The survival rate of transgenic plants under drought stress treatment is higher than that of wild-type plants. The results indicated that PeTIP3-2 was able to improve the drought resistance of plants. Our discovery lays the foundation for the functional study of AQPs in passion fruit.