Fading beauty: The protein degradation mechanism behind rose petal senescence

Sending a bouquet of roses to a loved one is a profoundly romantic gesture.While the desire for these beautiful blooms to last forever remains unattainable, the process of their natural fading can be prolonged.In this issue, Jingyun Lu, Guifang Zhang, and colleagues (Lu et al. 2024) provide a comprehensive understanding of how rose petal senescence is controlled at the molecular level.In their study, a new rose protein, SENESCENCE-ASSOCIATED F-BOX (RhSAF), was identified as a key player in mediating ethylene-induced petal senescence by destabilizing proteins involved in gibberellic acid (GA) signaling.Phytohormones, including ethylene and GA, intricately control various aspects of plant growth and development.Ethylene is recognized for its role in promoting petal senescence, while GAs function to repress this aging process (Ma et al. 2018).Ubiquitylation (also known as ubiquitination), a fundamental pathway for protein degradation in cells, involves ubiquitin ligases (or E3s), which direct the final transfer of the ubiquitin chain to the target proteins and are pivotal in most aspects of plant hormone signaling (Lechner et al. 2006, Kelley 2018).To search for ubiquitylation pathway genes that regulate flower senescence under ethylene influence, the researchers analyzed rose petal transcriptome data and found 19 F-box E3 protein genes upregulated under ethylene treatment.Among them, RhSAF stood out since it displayed increased transcription and expression levels during flower opening and senescence.Additional assays confirmed that RhSAF was induced by ethylene treatment and suppressed by an ethylene perception inhibitor.Using virus-induced gene silencing (VIGS) to silence RhSAF in rose petals resulted in delayed petal senescence.Additionally, a stable transgenic RNA interference (RNAi) line exhibited a prolonged petal lifespan when RhSAF expression was repressed.These findings suggest that RhSAF, induced by ethylene, plays a positive regulatory role in rose petal senescence.The RhSAF protein has a conserved F-box domain at its N-terminus, a nuclear localization signal (NLS), and a transmembrane domain at its C-terminus.Utilizing a transient fluorescent labeling approach, the authors confirmed that RhSAF localizes to both the nucleus and plasma membrane.Interaction studies between RhSAF and component proteins of S-PHASE KINASE-ASSOCIATED PROTEIN 1 (SKP1)-CUL1-F-box (SCF) type E3 ligase complex identified Rosa SKP1-like 4 (RSK4), RSK7, RSK12, and RSK20 as interactors of RhSAF, strongly suggesting that RhSAF is indeed a component of the SCF complex in roses.To look for target proteins ubiquitylated by RhSAF, the authors performed a yeast two-hybrid (Y2H) screen using a petal cDNA library as prey.GIBBERELLIN INSENSITIVE DWARF1B (RhGID1B) and RhGID1C emerged among the identified proteins.The in-planta interaction between RhSAF and RhGID1B/C was further validated by several independent methods and paved the way for a more precise functional characterization of this interaction.Co-expression experiments of GID1B/C