Date Published:

01

Abstract:

 TCPs are basic helix-loop-helix transcription factors. Arabidopsis (Arabidopsis thaliana) has 24 TCPs, 13 belong to Class I, and 11 to Class II (Martín-Trillo and Cubas, 2010). Class I TCPs promote, and Class II restrict, cell proliferation (Efroni et al., 2008). Previously, we showed that two Class I TCPs, TCP14 and TCP15 interact with the O-fucosyltransferase (OFT) SPINDLY (SPY) to promote cytokinin (CK) responses in young leaves and flowers (Steiner et al., 2012). SPY activity is required for TCP14 stability; the loss of SPY stimulates TCP14 proteolysis by the 26S proteasome and inhibits CK responses in flowers and leaves (Steiner et al., 2016). This is reversed by mutation in CULLIN1 (CUL1), suggesting a role for Skp, CUL1, F-box E3 ubiquitin ligase (SCF) complex in TCP14 proteolysis. OFT modify target proteins by transferring mono-fucose to serine and threonine residues (Holdener and Haltiwanger, 2019). SPY modifies the DELLA protein REPRESSOR OF ga1-3 (RGA) and increases its activity (Zentella et al., 2017). SPY also modifies PSEUDO RESPONSE REGULATOR5 (PRR5) and facilitates its proteolysis (Wang et al., 2020). Since mutation in the putative OFT catalytic domain of SPY (spy-3) is sufficient to reduce TCP14 stability, we suggested that O-fucosylation by SPY stabilizes TCP14. Here, we bring evidence that TCP14 interacts with the F-box proteins KISS ME DEADLY1 (KMD1), KMD2, and KMD4 (Kim et al., 2013) and this interaction promotes its degradation in the spy background. KMDs are negative regulators of CK signaling; they interact and destabilize the CK signaling components Type B RESPONSE REGULATOR (RR). Zhang et al. (2013) found that KMDs also target PHENYLALANINE AMMONIA LYASE (PAL) for degradation. Thus, although F-box proteins have high substrate specificity, KMDs seem to target several unrelated proteins.

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