Editing of two heat shock protein 70 genes enhances resistance of soybean to soybean cyst nematode

Heat shock protein 70 (HSP70) usually functions in maintaining protein homeostasis, and is also involved in regulating plant immunity, but mediation of plant-parasitic nematode resistance by HSP70s has rarely been reported. In this work, two high similarity soybean GmHSP70s [GmHSP70-13a (Glyma.13g254900) and GmHSP70-15a (Glyma.15g059900)] were studied in soybean cyst nematode (SCN) resistance, which is a devastating pathogen in soybean. Both GmHSP70-13a and GmHSP70-15a were significantly suppressed in resistant soybeans, compared to susceptible soybeans, at 0 day and 3 days post inoculation (dpi) of SCN. In soybean hairy roots, CRISPR/Cas9-editing of these two genes resulted in enhanced SCN resistance; accordingly, overexpressing either GmHSP70-13a or GmHSP70-15a suppressed SCN resistance. Both GmHSP70-13a and GmHSP70-15a interacted with GmSHMT08, which is one major SCN-resistant protein in soybeans and a key enzyme in one-carbon metabolism pathway. Compared to 0 dpi of SCN, at 3 dpi, GmHSP70-13a overexpression did not alter and GmHSP70-15a overexpression significantly suppressed, in contrast, the control remarkably promoted, GmSHMT08 expression in soybean. Furthermore, either GmHSP70-13a or GmHSP70-15a overexpression abnormally down-regulated expression of 4 one-carbon metabolism-associated genes (Glyma.06g235500, Glyma.12g015300, Glyma.15g071000, and Glyma.15g071200). Taken together, both GmHSP70-13a and GmHSP70-15a negatively mediated soybean SCN resistance likely by interacting with GmSHMT08, leading to GmSHMT08 suppression, along with impact of one-carbon metabolism pathway in soybean. This work provides 2 GmHSP70s gene-editing targets for soybean SCN resistance breeding. Overall design: RNA-seq profiling of soybean wildtype 'Williams 82' hairy roots (WT) and their over-expression lines (OE-Empty vector, OE-GmHSP70-13a and OE-GmHSP70-15a) at Day0 and Day3 of soybean cyst nematode infection.