Glycine max Sec61 complex genes function in the soybean defense response to the parasitic nematode Heterodera glycines

The Glycine max (soybean) secretory pathway performs important roles during the defense response to Heterodera glycines parasitism. However, the involvement of some aspects of the secretory machinery remains unexamined. The Sec61 complex of the eukaryote secretory pathway is composed of Sec61-α, Sec61-β, and Sec61-γ which bind, forming a trimeric complex that imports proteins into the ER for their processing, transport, and secretion. Comparative analyses using Saccharomyces cerevisiae Sec61-α, Sec61-β, and Sec61-γ protein sequences show G. max has homologs of each, 4 Sec61-α, 6 Sec61-β, and 4 Sec61-γ paralogs. At least one paralog from each gene family is expressed in H. glycines-parasitized G. max root cells during its defense process. GmSec61-α, GmSec61-β, and GmSec61-γ overexpression in the H. glycines-susceptible G. max_{[Williams 82/PI 518671]} leads to an engineered defense response. In contrast, RNAi of GmSec61-α, GmSec61-β, and GmSec61-γ in the H. glycines-resistant G. max_{[Peking/PI 548402]} generates susceptibility. The combined opposite outcomes of GmSec61 overexpression and RNAi provide evidence that they function in the defense process, consistent with the hypothesis that the G. max secretion system plays a role in its defense to H. glycines parasitism. The identification of Sec61-α, Sec61-β, and Sec61-γ homologs in 51 additional flowering plants spanning 20 Orders and 26 Families including the agriculturally-important Beta vulgaris ssp. vulgaris (sugar beet) demonstrates a potentially broad defense role not limited to these plant species. Computational studies identified genes encoding proteins having signal peptides in B. vulgaris parasitized by H. schachtii but undergoing a defense response further demonstrating the importance of Sec61 translocon in resistance.