a. flg22, PGN and Chitin activate GhMPK6 in cotton protoplasts. The protoplasts were transfected with GhMPK6, and incubated for 6 hr before treatment with different PAMPs for another 10 min. The concentrations of individual PAMPs are flg22, 1 uM; elf18, 1 uM; HrpZ1 harpin, 100 nM; PGN, 50 µg/ml; chitin, 50 µg/ml; LPS, 50 µg/ml; NPP1, 20 nM; VdNEP, 20 nM. His is the control of His-VdNEP. The top panel shows the MAPK activity detected by phosphorylation of MBP substrate, and the bottom panel is GhMPK6 expression detected by Western blot with an anti-HA antibody. b. flg22 activated AtMPK6, but not AtMPK4, in cotton protoplasts. c. flg22 activated GhMPK6 in Arabidopsis protoplasts. “-“ is the H2O control for flg22 and His is the control of His-VdNEP. d. ROS burst in cotton leaves triggered by flg22 treatment. The experiments were repeated three times with similar results. The data in (d) are shown as means ± standard errors from ten independent biological replicates.