Two coiled-coil regions of Xanthomonas oryzae pv. oryzae harpin differ in oligomerization and hypersensitive response induction

Abstract

Hpa1(Xoo) (harpin) is a type III secreted protein of the rice blight bacterial pathogen Xanthomonas oryzae pv. oryzae that elicits a hypersensitive response (HR) in nonhost tobacco. Hpa1(Xoo) is predicted to contain two potential coiled-coil (CC) regions, one at the N-terminus with a high probability of formation, and one at the C-terminus with a lower probability of formation. We constructed several CC-equivalent peptides by a chemosynthetic method, and investigated the structure-function of the predicted Hpa1(Xoo) CC regions, using biophysical and biochemical approaches. Both peptides elicited an HR in tobacco. Mutant versions of the N- and C-terminal peptides that were predicted to disrupt or favor CC formation were generated. The resulting altered HR activity and oligomerization indicated that the N-terminal CC region is essential for eliciting HR, but the C-terminus is not. The results also indicate that a 14-residue fragment (LDQLLCQLISALLQ) within the N-terminal CC region is a minimal and independent functional element for HR-induction in tobacco leaves. We propose that HR-induction requires a specific oligomerization of the CC regions of Hpa1(Xoo).

Hpa1 is a type III translocator in Xanthomonas oryzae pv. oryzae

“…The hpa1 and pthXo1 genes were deleted from PXO99 by using the unmarked deletion method [23]. Upstream and downstream flanking partial sequence fragments of hpa1 or pthXo1 were amplified from the PXO99 genomic DNA and connected together by overlapped fusion-PCR using specific primers (Additional file 1: Table S2).…”

“…Hpa1 comprises 139 amino acids with a molecular mass of 15 kD and carries a pair of α-helical coiled-coil motif at sites 37–52 and 87–102 [23]. While the N-terminal α-helix governs Hpa1 oligomerization [23], the first 53 residues determine its bioactivities in plants [5, 14, 24, 25].…”

“…While the N-terminal α-helix governs Hpa1 oligomerization [23], the first 53 residues determine its bioactivities in plants [5, 14, 24, 25]. Hpa1 affects virulence of the Xoo strain PXO99 in susceptible japonica rice variety Nipponbare [5] while the virulence is provided by the TAL effector PthXo1 [26].…”

Expression of hpa1 Gene Encoding a Bacterial Harpin Protein in Xanthomonas oryzae pv. oryzae Enhances Disease Resistance to Both Fungal and Bacterial Pathogens in Rice and Arabidopsis

“…oryzae causing bacterial leaf blight in rice (Zhu et al, 2000). It is a 13-kDa glycine-rich protein carrying two coiled-coil regions in its N-and C-termini (Ji et al, 2011). Its expression is regulated by HrpB, a regulatory protein that controls expression of other hrp (hypersensitive response and pathogenicity) genes in X. oryzae pv.…”

Biological significance and topological basis of aquaporin-partnering protein-protein interactions

“…15 This region contains the first of 2 a-helical coiled coils, 15 which potentially direct homogenous or heterogenous protein interactions, play an essential role in the oligomerization of type III translocators into the translocon, 39 and are also critical for the oligomerization of Hpa1 and its bioactivity in plants. [40][41][42][43] Hpa1 contributes to virulence of the Xoo strain PXO99…”