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The model plant Physcomitrium patens has played a pivotal role in enhancing our comprehension of plant evolution and development. However, the current genome harbours numerous regions that remain unfinished and erroneous. To address these issues, we generated an assembly using Oxford Nanopore reads and Hi-C mapping. The assembly incorporates telomeric and centromeric regions, thereby establishing it as a near telomere-to-telomere genome except a region in chromosome 1 that is not fully assembled due to its highly repetitive nature. This near telomere-to-telomere genome resolves the chromosome number at 26 and provides a gap-free genome assembly as well as updated gene models to aid future studies using this model organism., (© 2024. The Author(s), under exclusive licence to Springer Nature Limited.)

Plant genomes encode large numbers of F-box proteins (FBPs), the substrate recognition subunit of SKP1-CULLIN-F-box (SCF) ubiquitin ligases. There are ~700 FBPs in Arabidopsis , most of which are uncharacterized. TIR1 is among the best-studied plant FBPs and functions as a receptor for the plant hormone auxin. Here we use a yeast two-hybrid system to identify novel TIR1 mutants with altered properties. The analysis of these mutants reveals that TIR1 associates with the CULLIN1 (CUL1) subunit of the SCF through the N-terminal H1 helix of the F-box domain. Mutations that untether TIR1 from CUL1 stabilize the FBP and cause auxin resistance and associated growth defects, probably by protecting TIR1 substrates from degradation. Based on these results we propose that TIR1 is subject to autocatalytic degradation when assembled into an SCF. Further, our results suggest a general method for determining the physiological function of uncharacterized FBPs. Finally, we show that a key amino acid variation in the F-box domain of auxin signalling F-box (AFB1), a closely related FBP, reduces its ability to form an SCF, resulting in an increase in AFB1 levels.