Nucleoporin 160 Regulates Flowering through Anchoring HOS1 for Destabilizing CO in Arabidopsis

Abstract

Nuclear pore complexes (NPCs), which comprise multiple copies of nucleoporins (Nups), are large protein assemblies embedded in the nuclear envelope connecting the nucleus and cytoplasm. Although it has been known that Nups affect flowering in Arabidopsis , the underlying mechanisms are poorly understood. Here, we show that loss of function of Nucleoporin 160 ( Nup160 ) leads to increased abundance of CONSTANS (CO) protein and the resulting upregulation of FLOWERING LOCUS T ( FT ) specifically in the morning. We demonstrate that Nup160 regulates CO protein stability through affecting NPC localization of an E3-ubiquitin ligase, HIGH EXPRESSION OF OSMOTICALLY RESPONSIVE GENES1 (HOS1), which destabilizes CO protein in the morning period. Taken together, these results provide a mechanistic understanding of Nup function in the transition from vegetative to reproductive growth, suggesting that deposition of HOS1 at NPCs by Nup160 is essential for preventing precocious flowering in response to photoperiod in Arabidopsis .

Florigen trafficking integrates photoperiod and temperature signals in Arabidopsis

“…The E3 ubiquitin ligase HIGH EXPRESSION OF OSMOTICALLY RESPONSIVE GENE 1 (HOS1) negatively regulates CO abundance in the photoperiodic control of flowering and were insensitive to ambient temperature (Lazaro et al 2012;Lee et al 2012). The localization of HOS1 in nuclear pore complexes (NPC) is anchored by Nucleoporin 160 (Li et al 2020), suggesting the potential roles of NPC in integrating signals from photoperiod and thermosensory pathway. A MYB transcription factor EFM mediates the effect of ambient temperature and lightresponsive circadian clock on flowering and directly regulates FT expression (Yan et al 2014).…”

Regulation by FLOWERING LOCUS T and TERMINAL FLOWER 1 in Flowering Time and Plant Architecture

“…Thus, NPCs are involved in modulating CO protein levels and preventing precocious flowering in response to the photoperiod. [ 47,48 ] CO is also post‐translationally regulated by protein phosphorylation. The phosphorylated and unphosphorylated forms of CO proteins are detected throughout the day but in a variable ratio.…”

Nucleocytoplasmic Communication in Healthy and Diseased Plant Tissues

“…Whereas this phenotype might be related, at least in part, to defects in nuclear mRNA export (see chapter below), additional defects in protein stability and nuclear protein transport may contribute to the mutant phenotypes. In the case of NUP160 and NUP96, it was reported recently that both nucleoporins associate with and stabilize the E3-ubiquitin ligase HIGH EXPRESSION OF OSMOTICALLY RESPONSIVE GENES1 (HOS1) at the NPC ( Figure 2 and Table 2 ), which negatively regulates flowering transition via ubiquitination and subsequent proteasomal degradation of CO ( Cheng et al, 2020 ; Li et al, 2020 ). Loss of either HOS1 , NUP96 or NUP160 results in nuclear accumulation of CO and subsequent CO-mediated transcriptional activation of FLOWERING LOCUS T ( FT ).…”

“…Loss of either HOS1 , NUP96 or NUP160 results in nuclear accumulation of CO and subsequent CO-mediated transcriptional activation of FLOWERING LOCUS T ( FT ). FT induces the expression of genes that contribute to the formation of floral primordia, providing an explanation for the early flowering phenotypes of hos1 , nup96 and nup160 plants ( Cheng et al, 2020 ; Li et al, 2020 ).…”

“…While both, hos1 and nup160 plants, show an early flowering phenotype, the two mutants show opposite – i.e., enhanced ( hos1 ) and reduced ( nup160 ) – tolerance to cold stress ( Dong et al, 2006a , b ). Considering that NUP96 and NUP160 promote the stabilization and association of HOS1 at the NPC during flowering regulation ( Cheng et al, 2020 ; Li et al, 2020 ), a scenario of mutual NUP160-HOS1 stabilization at the NPC appears unlikely in cold stress signaling, and might be attributed to the dynamic nuclear accumulation of HOS1 in response to low temperature ( Lee et al, 2001 ). However, the localization of HOS1 has not been investigated in nup160 or nup96 plants grown under ambient or chilling/freezing conditions.…”