Functional analysis reveals the negative role of LrNCED5-1 and LrNCED5-2 in lily resistance to gray mold

Abscisic acid (ABA) plays a critical role in plant immune responses. The 9-cis-epoxy-carotenoid dioxygenase ( NCED ) gene family encodes pivotal rate-limiting enzymes in ABA biosynthesis. Although NCED family members have been identified in multiple plant species, genome-wide systematic analysis of NCEDs in Lilium spp. remains lacking. In this study, a total of 72 NCED genes were identified from the genomes of L. regale, L. sargentiae , and L. davidii var. unicolor . These genes were divided into five subgroups (Groups I–V) based on phylogenetic analysis. Examination of phylogenetic relationships and gene structures of lily NCEDs suggested potential functions in stress response. Transcriptome data analysis showed that most ABA biosynthesis and signaling genes exhibited higher transcript levels in Botrytis elliptica -infected susceptible lily than in resistant lily. Two ABA-responsive genes, LrNCED5–1 and LrNCED5–2 , were subsequently isolated from L. regale . qRT-PCR analysis confirmed that both genes displayed similar upregulated expression patterns upon B. elliptica inoculation. However, their expression levels in the susceptible cultivar ‘Tresor’ were significantly higher than those in the resistant L. regale . Transient overexpression of LrNCED5–1 and LrNCED5–2 in lily petals resulted in enhanced susceptibility to B. elliptica compared with the control. This increased susceptibility was accompanied by elevated ABA and gibberellin (GA 3 ) levels and decreased 1-aminocyclopropane-1-carboxylic acid (ACC) content, whereas silencing of LrNCED5–1 and LrNCED5–2 produced the opposite effect. Collectively, this study systematically identified NCED homologs in three Lilium species and demonstrated that LrNCED5–1 and LrNCED5–2 negatively regulated the gray mold resistance of lily petals.