Wheat Small GTPase Gene TaRABH1bL Is Involved in High-Temperature All-Stage Resistance to Puccinia striiformis f. sp. tritici.

As the largest subfamily of small GTPases, the Rab subfamily plays a pivotal role in regulating biotic and abiotic stresses in plants. However, the functions of Rabs in resistance to wheat stripe rust caused by Puccinia striiformis f. sp. tritici (Pst) remain unclear. Here, we identified a Rab subfamily gene, TaRABH1bL, from Xiaoyan 6 (XY6), a wheat cultivar known for non-race-specific and durable high-temperature all-stage (HTAS) resistance to stripe rust. The expression level of TaRABH1bL was exclusively up-regulated with Pst inoculation under the relatively high-temperature treatment, which indicated that TaRABH1bL might concurrently respond to both biotic and abiotic stress signals. The TaRABH1bL gene was primarily expressed in leaves. Barley stripe mosaic virus (BSMV)-induced TaRABH1bL gene silencing significantly reduced HTAS resistance to Pst, resulting in increased sporulation. Transient expression of TaRABH1bL in Nicotiana benthamiana leaves and wheat protoplasts confirmed its subcellular localisation in both cytoplasm and nuclei. The GTP-binding state of TaRABH1bL (TaRABH1bL) exclusively interacted with the transcription factor ethylene-responsive transcription factor 1-like (TaERF1L) in nuclei. TaERF1L directly bound to and suppressed the activity of the GCC-box motif, and this inhibitory effect was enhanced by the exclusive interaction between TaRABH1bL and TaERF1L. Silencing TaERF1L significantly reduced HTAS resistance. These results suggested that under dual signals of Pst infection and relatively high temperature treatment, TaRABH1bL transferred into its GTP-binding state and interacted with TaERF1L. Additionally, TaRABH1bL enhanced the suppression of TaERF1L on its downstream susceptible or temperature-sensitive genes containing the GCC-box motif, thereby activating HTAS resistance to Pst in XY6.