Hpa2

Hpa2 is a designation used in biology to refer to more than one protein across different organisms. In plant pathology, Hpa2 commonly denotes a hypersensitive response-associated protein 2, a member of the bacterial type III secretion system (T3SS) effector family. The precise function and even the exact protein sequence can vary between species, so Hpa2 does not describe a single universal protein.

In many Gram-negative plant pathogens, hpa2 genes are located within or near hrp/hrc pathogenicity islands and encode secreted effectors that are delivered into plant cells by the T3SS. Once inside host cells, Hpa2 proteins can modulate immune signaling, either suppressing basal defenses to promote virulence or, in some host genotypes, triggering defense responses such as the hypersensitive response. The outcome is highly host-dependent.

Structural and evolutionary features of Hpa2 members are variable. They are often small, cysteine-poor secreted proteins with little detectable homology to other families, and they typically lack obvious conserved motifs. Their coding sequences show rapid evolution, increasing diversity in order to adapt to different host targets and to escape plant surveillance systems.

Research on Hpa2 concentrates on understanding its role in virulence and host specificity, using approaches such as gene knockouts, localization studies, and interaction assays with plant proteins. Findings contribute to broader insights into how bacterial pathogens manipulate plant immunity and aid in breeding crops with durable resistance.