Supplementary Figure 1: Crystal structure and sequence alignment of THA8.

a, A cartoon diagram of THA8 is shown with rainbow color scheme from N-terminus (blue) to C-terminus (red). b, Superposition of THA8 (green, PDB code: 4ME2) and THA8L (magenta, PDB code: 4LEU) structures. The ribbon diagrams are shown for both structures. c, Sequence alignment of THA8 proteins from different species. BdTHA8, OsI-THA8, OsJ-THA8, ZmTHA8, SiTHA8 are THA8 protein sequences from Brachypodium distachyon, Oryza sativa Indica Group, Oryza sativa Japonica Group, Zea mays, and Setaria italica, respectively. Sequence alignment was performed by using ClustalW with manual adjustments. The secondary structure elements for BdTHA8 are noted on the top of the alignment. The conserved regions are highlighted in yellow. Residues making specific contacts with the G nucleotide are denoted with a black star; residues making contacts with the RNA backbone are denoted with a green star. Residues mediating critical dimer interactions are denoted with a magenta star. d, The BdTHA8 amino acid sequence is arranged as five PPR motifs. The predicted code residues in BdTHA8 are highlighted in blue (position 1 or 1') and yellow (position 6). The residues whose mutation severely impaired protein-RNA binding are colored in red whereas the residues whose mutation did not affect protein-RNA interaction are colored in green. The combination of T172 and D203 in positions 6 and 1' of motif 4 generates a specific code for G nucleotide.