Putative Serine Protease Effectors of Clavibacter michiganensis Induce a Hypersensitive Response in the Apoplast of Nicotiana Species

Abstract

Clavibacter michiganensis subspp. michiganensis and sepedonicus cause diseases on solanaceous crops. The genomes of both subspecies encode members of the pat-1 family of putative serine proteases known to function in virulence on host plants and induction of hypersensitive responses (HR) on nonhosts. One gene of this family in C. michiganensis subsp. sepedonicus, chp-7, is required for triggering HR in Nicotiana tabacum. Here, further investigation revealed that mutation of the putative catalytic serine residue at position 232 to threonine abolished the HR induction activity of Chp-7, suggesting that enzymatic activity is required. Purified Chp-7 triggered an HR in N. tabacum leaves in the absence of the pathogen, indicating Chp-7 itself is the HR elicitor from C. michiganensis subsp. sepedonicus. Ectopic expression of chp-7 constructs in N. tabacum leaves revealed that Chp-7 targeted to the apoplast triggered an HR while cytoplasmic Chp-7 did not, indicating that Chp-7 induces the HR in the apoplast of N. tabacum leaves. Chp-7 also induced HR in N. sylvestris, a progenitor of N. tabacum, but not in other Nicotiana species tested. ChpG, a related protein from C. michiganensis subsp. michiganensis, also triggered HR in N. tabacum and N. sylvestris. Unlike Chp-7, ChpG triggered HR in N. clevelandii and N. glutinosa.

Analysis of Extreme Phenotype Bulk Copy Number Variation (XP-CNV) Identified the Association of rp1 with Resistance to Goss's Wilt of Maize

“…In Gram-negative bacteria, many of the known effectors are delivered to plant cells through the type III systems (T3SS). However, no secretion systems equivalent to T3SS has been identified in Cmn (Bentley et al, 2008 ; Gartemann et al, 2008 ; Lu et al, 2015b ). The known virulence factors of related Clavibacter pathogens are secreted by the type II secretion system (T2SS).…”

A plant effector‐triggered immunity signaling sector is inhibited by pattern‐triggered immunity

“…The cAMP concentration was measured essentially as described previously (Lu et al, 2015). Inoculum of Pto D36E carrying AvrRpm1sp-Cya was prepared as described above and was infiltrated into the Arabidopsis leaves.…”

Multiple plasmid‐borne virulence genes of Clavibacter michiganensis ssp. capsici critical for disease development in pepper

“…Their role has also been reported to be associated with the colonization of host plants and the induction of the hypersensitive reaction in Nicotiana sp. (Stork et al, 2008;Lu et al, 2015a).…”

“…sepedonicus, putative virulence genes, including celA and celB genes, were up-regulated during potato infection (Burger et al, 2005;Holtsmark et al, 2008). In addition, the chp-7 gene is known as an important virulence factor for full virulence in a host and for induction of hypersensitive responses in a nonhost (Nissinen et al, 2009;Lu et al, 2015a).…”