Hop
(Hrp outer protein): Applies generically to all proteins secreted/translocated
by the Hrp system of P. syringae and other plant pathogens with similar
Hrp systems (e.g., Erwinia and Pantoea spp).
Avr
(Avirulence protein): Denotes a protein found through
the avirulence phenotype it confers on a P. syringae strain in appropriate
test plants. A shortcoming of the Avr designation is that the implied avirulence
phenotype is not always shared by homologs in other pathovars and strains. However,
many Avr names are deeply imbedded in the literature, and so it has been left
to the original lab of discovery to decide whether a given Avr family should be
incorporated into the new noemnclatural system
Hrp
(Hypersensitive response and pathogenicity): Most mutations in the TTSS machinery
abolish the ability of P. syringae to elicit the "HR" in nonhosts or
to be pathogenic in hosts. HrpA (the Hrp pilus subunit) represents a TTSS substrate
that retains its original designation because of its Hrp phenotype and/or association
with the Hrp system.
Effector:
A term for virulence proteins injected into host cells by a TTSS,
which is broadly applicable to various plant and animal pathogens.
Helper
Protein: A term of convenience referring to extracellular accessory
proteins (such as HrpA) plus other TTSS substrates (such as harpins) whose primary
function is likely to be the translocation of true effectors through host barriers.
Also called translocators.
Harpins:
Presumed helper proteins that are secreted by the TTSS in more abundance
than true effectors, appear to interact with plant cell walls and membranes, are
glycine-rich and devoid of cysteine, and possess a heat-stable ability to elicit
the hypersensitive response when infiltrated into the intercellular (apoplastic)
spaces of plant leaves.
TTSS:
Type III secretion pathway, also referred to as the Hrp pathway in P. syringae
pathovars. Secretion or translocation through this pathway is considered the defining
characteristic for P. syringae effector proteins
