Fig. 6: A model illustrating the origination, evolution, and function of ABA-independent PYL-like proteins.
From: ABA-independent PP2C-binding in PYLs traces to bacterial origins and persists in land plants
a Proposed stepwise evolution of PYL ABA receptors and ABA-independent PYL-like proteins. The ABA-independent PYL-like proteins originated horizontally from soil bacteria and exist in seeds of land plants. Two invariant lysine and leucine residues are crucial for the ABA responsiveness of PYL ABA receptors. PYL-like proteins gained PP2C-binding ability in some soil bacteria, and the ABA-independent PYL-like proteins obtained PP2C inhibitory activity before the last common ancestor of Zygnematophyceae and land plants. Although PYLs gained ABA-enhanced PP2C inhibition in bryophytes and evolved ABA-dependent PP2C inhibitory activity in mosses and angiosperms, some ABA-independent PYL-like proteins exist in vascular plants and are mainly expressed in dry seeds in plants such as Arabidopsis, Camelina, and Nicotiana attenuata. b Expression pattern of the ABA-independent PYL-like genes in dicot seeds. During seed maturation and desiccation, the expression of these ABA-independent PYL-like genes is gradually increased, probably functioning in basal stress signaling.
