80. Plant growth hormone receptors, namely TIR1, GID1, COI1 and PYL1 were knocked out independently in Arabidopsis plant. The resultant plants are named as tir1, gid1, coit and pyl1. Which one of the following statements regarding the above Arabidopsis plants is correct?
    (1) tirisdefective in ABA signaling while coil in gibberelline signaling
    (2) gid1 is defective in auxin signaling while pyll in JA signaling
    (3) coil is defective in JA signaling while pyllin ABA signaling
    (4) tir7 is defective in gibberellin signaling while gid1 in auxin signaling

    Correct answer: (3) coil is defective in JA signaling while pyll in ABA signaling

    Explanation:

    • TIR1 is the receptor for auxin; the tir1 mutant is defective in auxin signaling, not ABA.

    • GID1 is the receptor for gibberellin; the gid1 mutant is defective in gibberellin signaling, not auxin.

    • COI1 is the receptor for jasmonic acid (JA); the coi1 mutant is defective in JA signaling.

    • PYL1 is one of the receptors for abscisic acid (ABA); the pyl1 mutant is defective in ABA signaling.

    Option-wise:

    • (1) tir1 defective in ABA signaling — false. Coil defective in gibberellin — false.

    • (2) gid1 defective in auxin signaling — false. pyl1 in JA signaling — false.

    • (3) coil defective in JA signaling — true. pyl1 defective in ABA signaling — true.

    • (4) tir1 defective in gibberellin — false. gid1 in auxin signaling — false.

In Arabidopsis, TIR1 acts as an auxin receptor, GID1 as gibberellin receptor, COI1 as jasmonic acid receptor, and PYL1 as abscisic acid receptor; their mutants reveal pathway-specific defects such as coi1 in JA signaling and pyl1 in ABA signaling crucial for growth and stress responses.