Genome-wide identification and expression profiling of the MADS-box gene family in Lavandula angustifolia

MADS-box genes encode transcription factors critical for plant development, particularly floral organogenesis, flowering time regulation, and adaptation to environmental stresses. Among these, the MIKC^C-type genes are pivotal regulators in floral developmental processes. Although the evolutionary diversification and functional dynamics of MADS-box genes have been extensively characterized in model plants such as Arabidopsis thaliana and Oryza sativa, their evolutionary relationships and functional profiles in Lavandula angustifolia, an economically significant aromatic plant, remain poorly understood.

Genome-wide analysis identified 173 MADS-box genes in L. angustifolia, categorized into type I (Mα: 26; Mβ: 0; Mγ: 10) and type II (MIKC^C: 125; MIKC*: 12) based on phylogenetic comparisons with A. thaliana. The MIKC^C subgroup was further subdivided into 12 subclasses, including genes central to the ABCDE model of floral organ specification. Structural analyses revealed distinct conserved motifs and exon-intron configurations specific to each subgroup, indicative of functional divergence. Synteny analysis demonstrated Whole Genome Duplication (WGD) and segmental duplications as major contributors to MIKC^C gene family expansion, notably among genes linked to floral organ development. Expression profiling via RNA-seq and quantitative real-time PCR (qPCR) showed type II MADS-box genes exhibited higher expression levels with pronounced tissue-specific and developmental stage-specific expression patterns compared to type I genes. Many type II genes displayed significant associations with floral organogenesis, floral transition, and abiotic stress responses, underscoring their essential roles in reproductive development and environmental adaptability in L. angustifolia.

The identification and comprehensive characterization of 173 MADS-box genes in L. angustifolia highlight the significant expansion of the MIKC^C subgroup driven primarily by WGD and segmental duplications. The distinct structural features and specific expression patterns observed provide insights into the functional divergence and complexity of these genes, particularly regarding floral organogenesis and adaptation to environmental stress. This study establishes a robust molecular basis for further functional analysis and genetic improvement of aromatic plants.