Integrated proteomic, transcriptomic and metabolomic profiling reveals that GA-ABA hub runs the flower development in Chinese orchid Cymbidium sinense

Abstract

The seasonal flowering Chinese Cymbidium produce axillary floral meristem and require a dormancy period during cold conditions for flower development. However, their bud activation mechanism remains elusive. This study evaluates the multi-omics across six stages of flower development, along with functional analysis of core genes to decipher the innate mechanism of floral bud initiation and outgrowth in a Chinese orchid Cymbidium sinense. The transcriptome and proteome analyses identified 10 modules with essential roles in floral bud dormancy and activation. The gene clusters in the early stages of flower development were mainly related to flowering time regulation and meristem determination, while the late stages were correlated with hormone signaling pathways. The metabolome identified 69 potential hormones, wherein GA and ABA were the main regulatory hubs, and GA4 and GA53 exhibited a reciprocal loop. Extraneous GA application caused rapid elongation of flower buds and promoted the expression of flower development genes. Contrarily, exogenous ABA application extended the dormancy process, and ABA inhibitors indorsed dormancy release. Moreover, CsAPETALA1 (CsAP1) was identified as the potential target of ABA for floral bud activation. Transformation of CsAP1 in Arabidopsis and its transient overexpression in C. sinense protoplast not only affected the flowering time and floral organ morphogenesis in Arabidopsis but also orchestrated the expression of flowering and hormone regulatory genes. Presence of ABA response elements in the CsAP1 promoter, rapid downregulation of CsAP1 after exogenous ABA application and the activation of floral bud after ABA-inhibitor treatment suggest that ABA can control the bud outgrowth through CsAP1.