Two evolutionarily conserved residues of MED16 in 2 subclasses of angiosperms are important for pathogen response in Arabidopsis and rice. A) Frequency logos of partial amino acid sequences of MED16 in 33 different monocot and dicot species. The most prominent difference (PD signature in monocots vs. SE signature in dicots) is shown in Supplemental Fig. S4. PD signature: the proline (P) and aspartic acid (D) residues. SE signature: the serine (S) and glutamic acid (E) residues. B) Bacterial growth in atmed16, overexpressing 3 mutated AtMED16 transgenic lines. Bacterial titers were evaluated at 3 dpi. Data represent mean ± SE of 3 independent experiments, each consisting of 3 plants (n = 10). Letters represent statistically significant differences (P < 0.01; Duncan's multiple range test). These experiments were repeated twice with similar results. C) Leaf phenotypes of WT, spl38 mutant, and OsMED16M- or AtMED16M-overexpressing plants. The OsMED16M and AtMED16M cDNAs were introduced into spl38 plants, and T2 transgenic plants were generated. Leaves were collected and photographed at 60 d after germination. Scale bar, 1 cm. D) Chitin-induced MAPK activation in the leaves of 14-d-old WT and spl38 mutant seedlings. Leaves were treated with 10 μg mL⁻¹ chitin. Samples were collected at 0, 5, and 10 min, and analyzed by immunoblotting with anti-phospho-p44/42 MAPK antibody. Bands indicate phosphorylated MPK3 and MPK6 proteins. Coomassie brilliant blue staining of Rubisco served as a loading control. The experiments were repeated 3 times with similar results.