GmSHMT08-Mediated Soybean Cyst Nematode Resistance Is Negatively Modulated by Two Heat Shock Protein 70s in Soybean

The soybean GmSHMT08 (Rhg4) is a major gene conferring resistance to soybean cyst nematode (SCN), which is a devastating pathogen in soybean, yet its underlying resistance mechanism remains elusive. Heat shock protein 70 (HSP70) mainly functions in maintaining protein homoeostasis and regulating plant immunity. In this study, CRISPR/Cas9-mediated knockout of two highly similar GmHSP70s [GmHSP70-13a (Glyma.13g254900) and GmHSP70-15a (Glyma.15g059900)] enhanced, whereas overexpressing either of them suppressed, SCN resistance. Both GmHSP70-13a and GmHSP70-15a interacted with the key one-carbon metabolism enzyme GmSHMT08, and promoted GmSHMT08 degradation via 26S proteasome pathway, but neither of them altered GmSHMT08 transcript levels in soybean. Furthermore, both GmHSP70-13a and GmHSP70-15a were strongly induced in susceptible soybeans, while both of them still remained low in resistant soybeans, after SCN infection. Taken together, GmSHMT08-mediated SCN resistance is shown to be negatively modulated by both GmHSP70-13a and GmHSP70-15a. The regulation is facilitated through interacting with and influencing 26S proteasome system-involved degradation of GmSHMT08. This study elucidates a SCN-resistance mechanism of GmSHMT08, expands functions of HSP70s and provides two GmHSP70s gene-editing targets for soybean SCN resistance breeding.