Abstract:
Incompatible pathogen responses are frequently associated with cell death
in the host plant at the site of infection by pathogens and referred to as
hypersensitive response (HR). HR causes pathogen arrest and also leads to
activation of defence genes. Phospholipase A (PLA) is an important
enzyme group involved in many signal transduction pathways including
pathogen defence responses. Potential involvement of Arabidopsis thaliana
phospholipase. Genes namely, AtPLA IIA and AtPLA IIB in pathogen
responses was tested by transforming Petunia hybrida (Family Solanaceae)
for overexpression (sense) and suppression (antisense) of these genes.
Agrobacterium mediated leaf disc transformation method was employed to
produce transgenic Petunia. Development of HR was monitored in
detached leaves after inoculation with Pseudomonas syringae pv tomato
DC 3000. AtPLA IIA and AtPLA IIB overexpressing, suppressing and wild
type plants showed HR responses after 3-3.5 hrs, 6-6.5 hrs and 6-7 hrs of
pathogen inoculation respectively. Extensive spread of necrotic lesions was
observed in all the genotypes after 24-36 hrs, but severe necrotic lesions
were observed in overexpressing lines. Overexpression of AtPLA IIA and
AtPLA IIB genes have led to an accelerated and intense induction of HR
while antisense mediated suppression of the genes have led to relatively
slow induction of HR. The results revealed that constitutive overexpression
of AtPLA IIA and AtPLA IIB in transgenic Petunia enhances the HR
towards Pseudomonas syringae attack. It can be postulated that AtPLA IIA
and AtPLA IIB are involved in signal transduction pathway leading to the
HR.
