However, a PAN-like N-terminus exists only in the rosids and exclusively Brassicaceae homologs comprise four to five of the PAN N-terminal cysteines. TGA TFs with N-terminal extensions of variable length were identified in all analyzed seed plants. Comparative land plant analyses revealed that the AAGAAT motif exists in asterid and rosid plant species. Two N-terminal PAN cysteines, Cys68 and Cys87, were shown to form a disulfide bridge and Cys340, localized in a C-terminal putative transactivation domain, can be S-glutathionylated.

The redox-sensitive DNA-binding is mediated via a special PAN N-terminus, which is not present in other Arabidopsis TGA TFs and comprises five cysteines. Whereas PAN protein binds to this regulatory cis-element under reducing conditions, the interaction is strongly reduced under oxidizing conditions in EMSA studies. The AAGAAT motif is localized in the second intron of the floral homeotic regulator AGAMOUS ( AG), which controls stamen and carpel development as well as floral determinacy. Here, we investigated the DNA-binding of PAN to the AAGAAT motif under different redox-conditions. TGA proteins interact in the nucleus with land plant-specific glutaredoxins, which may alter their activities posttranslationally. For the TGA1 protein it was shown that several cysteines can be redox-dependently modified. The Arabidopsis TGA bZIP TF family comprises 10 members, of which PAN and TGA9/10 control flower developmental processes and TGA1/2/5/6 participate in stress-responses. The Arabidopsis TGA transcription factor (TF) PERIANTHIA ( PAN) regulates the formation of the floral organ primordia as revealed by the pan mutant forming an abnormal pentamerous arrangement of the outer three floral whorls. At Arabidopsis thaliana Al Arabidopsis lyrata Cr Capsella rubella Ag Arabis gunnisoniana Br Brassica rapa Bo Brassica oleracea Aa Aethionema arabicum Th Tarenaya hasseleriana Tc Theobroma cacao Gr Gossypium raimondii Pt Populus trichocarpa Gm Glycine max Md Malus domestica Fv Fragaria vesca Pp Prunus persica Eg Eucalyptus grandis St Solanum tuberosum Mg Mimulus guttatus Ug Utricularia gibba Ma Musa acuminata Os Oryza sativa Atr Amborella trichopoda Pa Picea abies Ppa Physcomitrella patens. The Oryza sativa AAGAAT motif (circle) was obtained from. The Aethionema arabicum motif originated from a BLAST result, indicated by a star symbol. The first position of the AAGAAT motif is variable. The blue box marks the characteristic AAGAAT sequence and the orange box the core TGA TF binding site.

The AAGAAT motif from the second Arabidopsis AG intron is indicated in bold. Comparison of sequences from plant species listed in S1 Table was conducted with the MacVector program. S2 Fig: Alignment of the AAGAAT motif from the analyzed AG-like intron regions.

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