Fig. 6. On the origin of LRR-RLPs and LRR-RLK-Xbs.

a Sequence similarity tree of IDs extracted from all LRR-containing PRRs. Branches are labelled in colours as indicated. Grey clade represents clade that contains both PSKR/PSY1R & BRI/BRL family, this clade is shown in b. In b, characterized LRR-RLK-Xb and LRR-RLP members are labelled. The BRI/BRL-clade, the PSKR clade, the PSY1R clade, and a clade with monocot-only IDs are labelled in different colours. In a, b, inner ring (Inner), middle ring (Middle) and outer ring (Outer) are labelled as indicated. Outer ring represents LRR-RLP and LRR-RLKs classification shown in Fig. 4d. In the outmost three rings, the presence of Kx5Y (Kx5Y), Yx8K (Yx8K), or either Kx5Y or Yx8K (Either) in the IDs are indicated in green, and absence of these motifs is indicated in grey. c Percentage (%) of IDs (before the last four LRR motifs) from LRR-RLP and LRR-RLK-Xb with the Kx5Y, Yx8KG, or either Kx5Y or Yx8KG (*) motifs. The Fisher test (2-sided) was performed to compare the number/fraction of IDs with either Kx5Y or Yx8KG in LRR-RLPs against LRR-RLK-Xb. The calculated p-value stated here (<1e-16) is too low to be given exact number. Thus, the upper bound limit is stated instead. d, g Structures and interaction interfaces of AtBRI1-Brassinosteroid (BR) and AtPSKR1-Phytosulfokine (PSK). Published structures of d AtBRL1-BR¹⁰⁰, g AtPSKR1-PSK⁴⁸ are shown. The left panels show the interaction sites between the LRR-RLK-Xb receptors and their ligands. Contacts are indicated by grey lines, hydrogen bonds are indicated by green dotted lines, and salt bridges are shown as cyan dotted lines. The positions of LRR residues (counting from C to N) are shown. Amino acid residues that are important for the interactions are highlighted in yellow and green, respectively. The right panel represents the 2D interaction network between the LRR-RLK-Xb receptors and their ligands. Contacts/interactions are shown in grey lines, hydrogen bonds are shown in green lines, and salt bridges are shown in cyan lines. Amino acids are labelled in colours according to their positions in the LRR motifs (counting from C to N). Structures were visualized in iCn3D⁹⁸. e, h Sequence similarity trees of the full-ectodomains of e BRI1/BRL clade and h PSKR clade from 350 species. Branches are labelled in colours as indicated in a. These trees are extracted from the BRI1/BRL and PSKR branches from Supplementary Fig. 16. In e, h, characterized LRR-RLK-Xb members are labelled. The LRR-RLK-Xb and LRR-RLP members taken for the alignment in f and i are also labelled in blue numbers (LRR-RLK-Xb) and pink numbers (LRR-RLP), respectively. f, i Ectodomain and alignment of multiple LRR-RLK-Xb and LRR-RLP members within the BRI1/BRL-clade extracted from e and the PSKR-clade extracted from h. f The alignment of ectodomain from LRR-RLK-Xb (blue) and LRR-RLP (pink) members taken from the sequence similarity tree in e. The orange highlights indicate the amino acids residues required from BR binding in AtBRI1, and the yellow highlights indicate the amino acid residues required for BR binding in AtBRL1¹⁰⁰. The yellow highlights are corresponding to the amino acids highlighted in the structure in d. The LRR motifs and ID in the alignment are indicated in colours shown in d (the interaction network; right panel). i The alignment of ectodomain from LRR-RLK-Xb (blue) and LRR-RLP (pink) members taken from the sequence similarity tree in h. The green highlights indicate the amino acids residues required from PSK binding in AtPSKR1⁴⁸. The green highlights are corresponding to the amino acids highlighted in the structure in g. The LRR motifs and ID in the alignment are indicated in colours shown in g (the interaction network; right panel). Due to space limitation, the last 9 amino acids in each LRR motif are presented as * in the alignment. For the full alignment, refer to Supplementary Fig. 17a.