Figure 7.

Model for the Parallel SA Action in Immunity and Growth Regulation

(A) SA plays a key role in the growth-immunity transition following pathogen attack: on one hand, SA activates the immune response, through stimulating NPR1 and repressing NPR3/4, all together increasing the expression of downstream defense genes; on the other hand, SA inhibits growth via suppressing PP2A activity and the subsequent dephosphorylation of substrates.

(B) The auxin efflux carrier PIN2 is phosphorylated by different kinases, including PINOID/WAGs, D6PK/D6PKLs, and MAPKs, and dephosphorylated by PP2A. Following pathogen attack, the SA levels increase. SA binds to the A subunits of PP2A and thereafter represses its dephosphorylation activity toward PIN proteins, which leads to hyperphosphorylation of PIN, thereby a decrease in PIN activity ultimately resulting in a decrease in auxin export and attenuation of growth.

(C and D) Induced stronger expression of pPR1::eYFP-NLS by SA was detected in pp2aa1-6.

(C) pPR1::eYFP-NLS seedlings were constantly grown on plates with DMSO or 40 μM SA for 5 days from germination and were then imaged by CLSM. Scale bars, 10 μm.

(D) For quantification, the average GFP florescence of 5–10 representative cells from 10 seedlings for each treatment was measured by Fiji. The data points were showed as dot plots, and lines indicate mean ± SD. Different letters represent significant difference; p < 0.05; by one-way ANOVA with a Tukey multiple comparison test.