Identification of proteins regulated by cross-talk between drought and hormone pathways in Arabidopsis wild-type and auxin-insensitive mutants, axr1 and axr2.

Ten proteins differentially regulated by progressive drought stress in Arabidopsis Columbia wild-type, axr1-3 and axr2-1auxin-insensitive mutants, were identified from internal amino acid microsequencing. These proteins fell into two categories: (i) stress-related proteins, known to be induced by rapid water stress via abscisic acid (ABA)-dependent or -independent pathways [late embryogenesis abundant (LEA)-like and heat shock cognate (HS) 70, respectively], or in response to pathogens or oxidative stress [β-1,3 glucanase (BG), annexin] and (ii) metabolic enzymes [glutamine synthetase (GS), fructokinase (Frk), caffeoyl-CoA-3-O-methyltransferase (CCoAOMT)]. The differential behaviour of these proteins highlighted a role for AXR2 and/or AXR1 in the regulation of their abundance during drought adaptation. In particular, reduced induction of RD29B, GS and annexin, and overexpression of BG2 were observed specifically in the axr1-3 mutant, which is dramatically affected in several ABA-dependent drought adaptive responses, such as drought rhizogenesis. Altogether these results indicate cross-talk between auxin- and ABA-signalling in Arabidopsis drought responses.