Figure 2.

SA regulates auxin distribution in Arabidopsis thaliana root. An SA treatment activates the auxin biosynthetic enzyme TAA1 and inhibits the PIN2/PIN7 auxin efflux carriers. Low doses of SA activate PIN1, promoting auxin accumulation and transportation, which leads to a distal meristem extension. High doses of SA decrease PIN1 expression, inhibiting meristem activity. Moreover, SA elevates PIN2 phosphorylation, thereby affecting auxin transport. TAA1, TRP AMINOTRANSFERASE OF ARABIDOPSIS 1; PIN1/2/4/7, PIN-FORMED 1/2/4/7; PP2AA1, Protein Phosphatase 2A subunit A; PID, Protein kinase PINOID; P, phosphate; RAM, root apical meristem.