Abscisic acid inhibits root growth in Arabidopsis through ethylene biosynthesis

Abstract

Summary: When first discovered in 1963, abscisic acid (ABA) was called abscisin II because it promotes abscission. Later, researchers found that ABA accelerates abscission via ethylene. In Arabidopsis, previous studies have shown that high concentrations of ABA inhibit root growth through ethylene signaling but not ethylene production. In the present study in Arabidopsis, we found that ABA inhibits root growth by promoting ethylene biosynthesis. The ethylene biosynthesis inhibitor L–α–(2‐aminoethoxyvinyl)‐glycine reduces ABA inhibition of root growth, and multiple mutants of ACS (1–aminocyclopropane‐1–carboxylate synthase) are more resistant to ABA in terms of root growth than the wild‐type is. Two ABA‐activated calcium‐dependent protein kinases, CPK 4 and CPK 11, phosphorylate the C–terminus of ACS 6 and increase the stability of ACS 6 in ethylene biosynthesis. Plants expressing an ACS 6 mutant that mimics the phosphorylated form of ACS 6 produce more ethylene than the wild‐type. Our results reveal an important mechanism by which ABA promotes ethylene production. This mechanism may be highly conserved among higher plants.