The following statements are made about the involvement of the type III protein secretion system (T3SS) during bacterial pathogenesis in plants and animals.

A. It involves a protein complex that spans both the inner and outer bacterial membranes.
B. T3SS mostly secretes Avr effector proteins directly into plant apoplast.
C. The genes encoding conserved components of the T3SS of plant and animal pathogenic bacteria are referred to as Hrp (hypersensitive response and pathogenicity cluster).
D. Once Avr effectors are delivered inside the plant cell, Hrp proteins are not needed for the activation of the defense response.

Which one of the following options represents the combination of all correct statements?

Correct option is C

EXPLANATION-

Statement A- It involves a protein complex that spans both the inner and outer bacterial membranes.

Correct – The T3SS forms a needle-like complex (injectisome) that spans both membranes in Gram-negative bacteria to transport effector proteins into host cells.

Statement B- T3SS mostly secretes Avr effector proteins directly into plant apoplast.
 Incorrect – T3SS delivers Avr effector proteins directly into the host cell cytoplasm, not just the apoplast (the space outside the plasma membrane). The apoplast is not the typical target of T3SS injection.

Statement C: The genes encoding conserved components of the T3SS of plant and animal pathogenic bacteria are referred to as hrp (hypersensitive response and pathogenicity cluster).
Correct – True for many plant pathogens. hrp genes are well-known components involved in T3SS machinery.

Statement D- Once Avr effectors are delivered inside the plant cell, Hrp proteins are not needed for the activation of the defense response.
 Correct – Hrp proteins are involved in the delivery process. Once inside, the effectors themselves interact with the host cell machinery to trigger or suppress defense responses. So Hrp proteins are not directly required for the host's defense activation.

So, the correct option is (c)  A and D is correct.