Nup96 and HOS1 Are Mutually Stabilized and Gate CONSTANS Protein Level, Conferring Long-Day Photoperiodic Flowering Regulation in Arabidopsis

Abstract

The nuclear pore complex profoundly affects the timing of flowering; however, the underlying mechanisms are poorly understood. Here, we report that Nucleoporin96 (Nup96) acts as a negative regulator of long-day photoperiodic flowering in Arabidopsis (Arabidopsis thaliana). Through multiple approaches, we identified the E3 ubiquitin ligase HIGH EXPRESSION OF OSMOTICALLY RESPONSIVE GENE1 (HOS1) and demonstrated its interaction in vivo with Nup96. Nup96 and HOS1 mainly localize and interact on the nuclear membrane. Loss of function of Nup96 leads to destruction of HOS1 proteins without a change in their mRNA abundance, which results in overaccumulation of the key activator of long-day photoperiodic flowering, CONSTANS (CO) proteins, as previously reported in hos1 mutants. Unexpectedly, mutation of HOS1 strikingly diminishes Nup96 protein level, suggesting that Nup96 and HOS1 are mutually stabilized and thus form a novel repressive module that regulates CO protein turnover. Therefore, the nup96 and hos1 single and nup96 hos1 double mutants have highly similar early-flowering phenotypes and overlapping transcriptome changes. Together, this study reveals a repression mechanism in which the Nup96-HOS1 repressive module gates the level of CO proteins and thereby prevents precocious flowering in long-day conditions.

Nuclear pore complex components have temperature‐influenced roles in plant growth and immunity

“…A large overlap between DEGs of nup96 and hos1 mutants were observed at 28°C (Figure a–c, Figure S4), indicating a similar role in transcriptome reprogramming at high temperature. This is consistent with the recent finding that NUP96 and HOS1 proteins are mutually stabilized, and they regulate similar biological pathways in some cases (Cheng et al, ). It is yet to be determined if other nup mutants with a high temperature defect also have this transcriptome pattern.…”

B-box transcription factor 28 regulates flowering by interacting with constans

“…Photoreceptors Phytochrome B (PHYB) and Zeitlupe (ZTL) destabilize CO in the morning while Phytochrome A (PHYA), Cryptochromes (CRYs) and Flavin-Binding, Kelch Repeat F-box1 (FKF1) stabilize CO in the afternoon under LD 10 – 13 . The interaction between Nucleoporin 96 (Nup 96) and HOS1 and their mutual stabilization form a novel repressive module to gate CO protein level in Arabidopsis under LD 14 . GIGANTEA (GI) plays a pivotal regulation on the timing stabilization of CO by altering FKF1-ZTL interaction 15 .…”

Genomic identification and expression analysis of nuclear pore proteins in Malus domestica

“…6). Previous studies have confirmed that some Nups (AtNup54, AtNup62, AtNup96, AtNup160, and AtHOS1) affect flowering time in Arabidopsis thaliana 1,[23][24][25] . And the tissue-specificity analysis found that MdNup54, MdNup62, MdNup133, and MdNup160 were most highly expressed in buds, and MdNup93 was also highly expressed in buds, suggesting that these genes may be involved in the apple flowering pathway.…”

“…However, Tissue specific expression only provides reference for the potential function of Nups, which need to be experimentally verified. Arabidopsis thaliana studies have confirmed that some Nups (AtNup54, AtNup62, AtNup96, AtNup160, and AtHOS1) affect flowering time 1,[23][24][25] . However, little is known about their potential roles in apple-induced flowering.…”

“…An investigation of A. thaliana proved that Nup96 promotes the stability of HOS1, which binds to and degrades CO, resulting in delayed flowering. Moreover, HOS1 increases the stability of Nup96, thereby maintaining this regulatory pathway to control flowering time 25 .…”