Functional and Transcriptome Analysis Reveal Specific Roles of Dimocarpus longan DlRan3A and DlRan3B in Root Hair Development, Reproductive Growth, and Stress Tolerance

Ran GTPases play essential roles in plant growth and development. Our previous studies revealed the nuclear localization of DlRan3A and DlRan3B proteins and proposed their functional redundancy and distinction in Dimocarpus longan somatic embryogenesis, hormone, and abiotic stress responses. To further explore the possible roles of DlRan3A and DlRan3B, gene expression analysis by qPCR showed that their transcripts were both more abundant in the early embryo and pulp in longan. Heterologous expression of DlRan3A driven by its own previously cloned promoter led to stunted growth, increased root hair density, abnormal fruits, bigger seeds, and enhanced abiotic stress tolerance. Conversely, constitutive promoter CaMV 35S (35S)-driven expression of DlRan3A, 35S, or DlRan3B promoter-controlled expression of DlRan3B did not induce the alterations in growth phenotype, while they rendered different hypersensitivities to abiotic stresses. Based on the transcriptome profiling of longan Ran overexpression in tobacco plants, we propose new mechanisms of the Ran-mediated regulation of genes associated with cell wall biosynthesis and expansion. Also, the transgenic plants expressing DlRan3A or DlRan3B genes controlled by 35S or by their own promoter all exhibited altered mRNA levels of stress-related and transcription factor genes. Moreover, DlRan3A overexpressors were more tolerant to salinity, osmotic, and heat stresses, accompanied by upregulation of oxidation-related genes, possibly involving the Ran-RBOH-CIPK network. Analysis of a subset of selected genes from the Ran transcriptome identified possible cold stress-related roles of brassinosteroid (BR)-responsive genes. The marked presence of genes related to cell wall biosynthesis and expansion, hormone, and defense responses highlighted their close regulatory association with Ran.