Activation of Self-Incompatibility Signaling in TransgenicArabidopsis thalianaIs Independent of AP2-Based Clathrin-Mediated Endocytosis

Abstract

Internalization of plasma membrane (PM)-localized ligand-activated receptor kinases and their trafficking to sorting endosomes have traditionally been viewed as functioning primarily in the down-regulation of receptor signaling, but are now considered to be also essential for signaling by some receptors. A major mechanism for internalization of PM proteins is clathrin-mediated endocytosis (CME). CME is mediated by the Adaptor Protein Complex 2 (AP2), which is involved in interaction of the AP2 μ-adaptin subunit with a tyrosine-based Yxxϕ motif located in the cytoplasmic domain of the cargo protein. In this study, we investigated the role of AP2-mediated CME for signaling by the S-locus receptor kinase (SRK), a protein localized in the PM of stigma epidermal cells, which, together with its pollen coat-localized S-locus cysteine-rich (SCR) ligand, functions in the self-incompatibility (SI) response of the Brassicaceae. Using Arabidopsis thaliana plants that were made self-incompatible by transformation with an A. lyrata-derived SRK/SCR gene pair, we tested the effect on SI of site-directed mutations in each of the two Yxxϕ motifs in SRK and of a CRISPR/Cas9-induced null mutation in the AP2 μ-adaptin gene AP2M. Both in vitro SRK kinase activity and the in planta SI response were abolished by substitution of tyrosine in one of the two Yxxϕ motifs, but were unaffected by elimination of either the second Yxxϕ motif or AP2M function. Thus, AP2-mediated CME is considered to be unnecessary for SRK signaling in the SI response.

Reproductive phasiRNAs regulate reprogramming of gene expression and meiotic progression in rice

“…The S-RLK proteins determine self-incompatibility responses in self-incompatible plants. In self-compatible plants, S-RLK expression is suppressed in the anthers, which might be a pre-requisite for self-pollination, because the overexpression of S-RLKs in self-compatible plants often suppresses self-pollination 41 . We have also shown that high expression levels of the phasiRNA target genes negatively regulate sporogenesis and seed setting, and reproductive phasiRNAs are involved in suppressing these RLKs.…”

Chloride Channel Family in the Euhalophyte Suaeda altissima (L.) Pall: Cloning of Novel Members SaCLCa2 and SaCLCc2, General Characterization of the Family

“…In N- and C-terminal domains located to cytoplasm of SaCLCa2, SaCLCc2, as well as of other SaCLC proteins consensus tyrosine-based motifs YXXΦ (Φ is a hydrophobic amino acid) and dileucine-based motifs DXXLL or [DE]XXXL[LI] were found ( Figure 1 , underlined). A key role of similar motifs in sorting and subcellular localization was shown for a number of membrane A. thaliana proteins [ 40 , 41 , 42 , 43 , 44 , 45 ].…”

“…These recruit components of the transport machinery, ensuring delivery of proteins to proper membranes [ 45 , 50 , 51 ]. Involvement of tyrosine- and dileucine-based motifs in sorting and control of subcellular localization of endocytosed plant proteins, such as auxin transporter PIN1 [ 40 ], vacuolar sorting receptor VSR4 [ 41 ], brassinosteroid receptor BRI1 [ 44 ], vacuolar transporters NRAMP3 и NRAMP4 [ 42 ], and SRK kinase [ 43 ], has been demonstrated. Analyses of amino acid sequences in S. altissima CLC proteins displayed presence of similar consensus motifs in N- and C-terminal domains located to cytoplasm ( Figure 1 , underlined).…”