Suppressing wheat sucrose phosphate synthase 1-B protects wheat against stripe rust.

INTRODUCTION: Stripe rust caused by Puccinia striiformis Westend. f. sp. tritici (Pst) is a highly destructive wheat disease that threatens global food security. Pst extracts energy from wheat by interfering with photosynthesis, leading to significant yield losses. Redirecting metabolite flux to counteract pathogens remains a major challenge in enhancing crop resilience. OBJECTIVE: The primary objective of this study is to clarify the regulations of sucrose synthesis in wheat during its interaction with Pst, especially in relation to susceptibility and resistance response, and to supply genetic resources for breeding programs dedicated to ensuring food security. METHODS: Utilizing bulked segregant RNA sequencing (BSR-Seq), we identified and cloned a novel susceptibility (S) gene, sucrose 6 - phosphate synthase 1 (SPS1). We investigated the transcriptional and post-translational regulations of SPS1 by Pst, the wheat APETALA2 transcription factor (wAP2), and Wheat Kinase START 1 (WKS1, Yr36) in transgenic plants using molecular and biochemical approaches. Sugar content variations were analyzed using gas chromatography-mass spectrometry (GC/MS) and colorimetric assays, while Pst infection dynamics were examined by staining or quantifying biomass and uredinial pustule densities. RESULTS: Targeted mutagenesis of the Pst-inducible SPS1-B gene significantly reduced sucrose content accumulation and restricted Pst growth without compromising yield. In contrast, over-expressing SPS1-B enhanced Pst growth, confirming its role as a susceptibility (S) gene to Pst. Pst upregulated SPS1-B under optimal conditions, enhancing its own pathogenic success. Conversely, wAP2 suppressed SPS1-B transcription, reduced SPS1 protein level, and inhibited Pst infection intensity in transgenic wheat lines. Moreover, WKS1, a high-temperature adult-plant resistance protein, bound, phosphorylated, and suppressed SPS1-B at the post-translational level. CONCLUSION: This study identifies SPS1-B as a pivotal molecular switch in sucrose metabolism hijacked by Pst to support its infection. The characterization of SPS1-B and its upstream regulators provides multiple genetic targets for enhancing wheat resistance against stripe rust.