ICE‐SCREAM comes in different flavors: Angiosperms encode two types of ICE proteins predicted to differ in their regulation by OST1 and MPK3/6

Abstract

AbstractINDUCER OF CBF EXPRESSION (ICE) proteins reportedly have a role in cold acclimation and stomata development, but the former has recently been questioned. Our aim was to analyze ICE, OPEN STOMATA 1 (OST1) and MITOGEN ACTIVATED PROTEIN KINASE 3/6 (MPK3/6) protein data and place the results in context with reports in the literature. Orthologous protein sequences from species representative of different plant lineages were retrieved via BLAST searches and assembled into multiple sequence alignments for a comprehensive comparison of key features. We identified one type of ICE protein in bryophytes, lycophytes, ferns and angiosperms, and a second type of ICE protein in angiosperms only, each with characteristic interaction domains. Due to the higher observed similarity of the identified orthologs to proteins from Vitis riparia than to those from Arabidopsis, they were referred to as VrICE2L and VrICE4L, respectively. Regulatory sequence motifs for the kinase OST1 were present in the VrICE2L proteins although less conserved in the non‐angiosperms, whereas OST1 orthologs could be identified in all plant species, including algae. Interestingly, MPK3/6 motifs were most clearly conserved in the VrICE2L and VrICE4L proteins of the more evolved angiosperms, at a time that the A subtype of MPK3/6 kinases and the CRT‐BINDING FACTOR (CBF)‐encoding genes first appeared in the plant lineages. These data are intended to stimulate further investigations of VrICE4L proteins in non‐model plants and provide some evolutionary context into the overlap between stomatal function and regulation, and the cold acclimation pathway.