The Diverse Salt-Stress Response of Arabidopsis and Ethylene Signaling Mutants Is Linked to Altered Root Auxin Homeostasis.

We explored the interplay between ethylene signals and the auxin pool in roots exposed to high salinity using wild-type plants (Col-0), and the ethylene-signaling mutants (constitutive) and (insensitive). The negative effect of salt stress was less pronounced in individuals, which was concomitant with augmented auxin signaling both in the controls and after 100 mM NaCl treatment. The R2D2 auxin sensorallowed mapping this active auxin increase to the root epidermal cells in the late Cell Division (CDZ) and Transition Zone (TZ). In contrast, the ethylene-insensitive plants appeared depleted in active auxins. The involvement of ethylene/auxin crosstalk in the salt stress response was evaluated by introducing auxin reporters for local biosynthesis () and polar transport (, , , , ) in the mutants. The constantly operating ethylene-signaling pathway in was linked to increased auxin biosynthesis. This was accompanied by a steady expression of the auxin transporters evaluated by qRT-PCR and crosses with the auxin transport reporters. The results imply that the ability of mutant to tolerate high salinity could be related to the altered ethylene/auxin regulatory loop manifested by a stabilized local auxin biosynthesis and transport.