Functional characterization of gibberellin in controlling flowering time in loquat (Eriobotrya japonica) with autumn and spring flowering habits

Flowering represents a critical morphological transition from vegetative to reproductive growth in plants, and optimal timing of this process is essential for loquat ( Eriobotrya japonica ) production to mitigate natural disasters while improving fruit quality and yield. In this study, comparative phenological and anatomical analyses between autumn-flowering and spring-flowering loquat cultivars revealed that the variation in flowering time primarily stems from differences in both the initiation of floral bud differentiation and the development of inflorescence lateral axes. Morphological differentiation timing was identified as the predominant factor influencing flowering period divergence. Transcriptome profiling of floral development in autumn-flowering ('Guozhenhao 3') and spring-flowering ('Chunhua No.1') loquat cultivars revealed that the late morphological development stage exhibited the highest number of differentially expressed genes, which were significantly enriched in pathways related to floral organ development, whorl formation, and gibberellin (GA) signal transduction. Weighted Gene Co-expression Network Analysis (WGCNA) of differentially expressed genes (DEGs), hormones, and flowering time identified four DELLA genes repressed by gibberellin signaling. The two loquat cultivars exhibited distinct endogenous gibberellin dynamics during floral bud differentiation. Exogenous GA 3 application during early morphological differentiation in two loquat cultivars promoted floral development and early flowering through coordinated regulation of GA biosynthesis genes ( C19-GA2OX1 , C20-GA2OX1 , GA3OX , GA20OX ), the GA signaling repressor DELLA ( EjRGL3a ), and flowering integrators ( EjAGL24 , EjLFY ). EjRGL3a silencing during early bud differentiation accelerated flowering and upregulated floral integrators ( EjAP1 , EjLFY , EjAGL24 ) in two loquat cultivars. These findings provide mechanistic insights into the regulatory role of gibberellin in loquat flowering. • The speed of inflorescence axis development is the primary factor affecting the flowering time difference between spring- and autumn-flowering loquats. • Transcriptomic divergence between CH1 and GZH3 shows significant enrichment in GO terms associated with gibberellin response, floral organ development, and floral whorl development. • Exogenous GA 3 application during morphological differentiation accelerates flowering. • WGCNA identifies four DELLA genes as GA-signaling repressors, with functional validation of EjRGL3a ( DELLA ) as a novel flowering-time regulator in loquat.