SAUR21-like genes in broccoli and Arabidopsis: Comparative expression and functional characterization

The Small Auxin Up-Regulated RNA (SAUR) gene family has been implicated in various physiological processes in plants, including auxin signaling, senescence, and stress tolerance. Our previous genome-wide transcriptional analyses on postharvest senescence in broccoli (Brassica oleracea L.) identified the BoSAUR gene family as a key regulator in this process. In this study, we examined the expression patterns of BoSAUR family genes under various treatments aimed at delaying postharvest senescence of broccoli, analyzing its protein structure and phylogenetic relationship within the BoSAUR family.

We applied gene expression, protein structure, phylogenetic analysis, and mutant characterization to investigate SAUR genes and their roles in senescence. Genome sequences of broccoli were retrieved for identifying BoSAUR genes, followed by phylogenetic, motif, and gene structure analyses using tools like MEME and GSDS. Promoter regions were analyzed with PlantCARE, and chromosomal locations were mapped using TBtools. A T-DNA insertion mutant of SAUR21 gene in Arabidopsis was analyzed for functional analysis.

We found that BoSAUR21-like (LOC106327409) was consistently downregulated during natural and postharvest senescence across all treatments, regardless of ethylene status, identifying it as a core senescence-associated gene in broccoli. Genome-wide analysis identified that the BoSAUR21-like gene family shares a single-exon architecture with conserved SAUR motifs. To infer the function of BoSAUR21-like, we characterized the Arabidopsis AtSAUR21 T-DNA insertion mutant, a homologue of BoSAUR21-like. Phenotypic analysis of this mutant revealed accelerated leaf senescence, early bolting, and enhanced chlorophyll degradation compared to wild-type, suggesting that the orthologous BoSAUR21-like gene family likely plays a conserved role in senescence regulation in broccoli.

These findings establish BoSAUR21-like gene as a promising candidate for genetic manipulation aimed at delaying postharvest senescence in broccoli and other Brassica crops. Future work should include direct functional characterization of BoSAUR21-like in broccoli through CRISPR-Cas9 knockout and overexpression approaches to confirm its role and assess its potential for extending postharvest shelf life.