Catalpa bungei, a tree indigenous to China, is renowned for its superior timber quality and as an ornamental in horticulture. To promote the cultivation of C. bungei in cold regions and expand its distribution, enhancing its cold tolerance is essential. The CCCH gene family is widely involved in plant growth, development, and expression under stress conditions, including low-temperature stress. However, a comprehensive identification and analysis of these genes have not yet been conducted. This study aims to identify key cold-tolerance-related genes within the CCCH gene family of C. bungei, providing the necessary theoretical support for its expansion in cold regions. In this study, 61 CCCH genes within C. bungei were identified and characterized. Phylogenetic assessment divided these genes into 9 subfamilies, with 55 members mapped across 16 chromosomes. The analysis of gene structures and protein motifs indicated that members within the same subfamily shared similar exon/intron distribution and motif patterns, supporting the phylogenetic classification. Collinearity analysis suggested that segmental duplications have played a significant role in the expansion of the C. bungei CCCH gene family. Notably, RNA sequencing analysis under 4 °C cold stress conditions identified CbuC3H24 and CbuC3H58 as exhibiting the most significant responses, highlighting their importance within the CCCH zinc finger family in response to cold stress. The findings of this study lay a theoretical foundation for further exploring the mechanisms of cold tolerance in C. bungei, providing crucial insights for its cultivation in cold regions.

To overcome the seasonal constraints of explant availability and facilitate genetic improvement in Catalpa ovata, this study established a dual-pathway in vitro regeneration system (encompassing adventitious shoot organogenesis and somatic embryogenesis) using mature zygotic embryos. We systematically evaluated the synergistic effects of maternal genotypes, plant growth regulators (PGRs), basal media, and the histone deacetylase inhibitor Trichostatin A (TSA). Genotype screening revealed significant divergence in regenerative potential, with the half-sib family 32F17 exhibiting superior responsiveness (84.7% callus induction). A high cytokinin-to-auxin ratio (ZA3 medium) optimally drove direct shoot organogenesis. For adventitious shoot proliferation, the addition of TDZ significantly improved the multiplication coefficient (up to 2.99 on ZB4 medium), although a physiological trade-off with shoot elongation was observed. In parallel, the application of 10 µM TSA significantly enhanced somatic embryogenesis from embryogenic calli, effectively alleviating the inhibitory constraints of exogenous PGRs. For rhizogenesis, the DKW basal medium proved superior to half-strength MS, with the ZE3 treatment (0.1 mg·L⁻¹ NAA + 0.1 mg·L⁻¹ IBA) yielding the highest rooting frequency (69.6%) and robust root architecture. Notably, while somatic embryo conversion remained recalcitrant, plantlets derived exclusively from the adventitious shoot organogenesis pathway were successfully acclimatized ex vitro. These transplanted plantlets exhibited consistently high survival rates (83.1–84.4%) across all tested genotypes, effectively overcoming the initial genotype-dependent recalcitrance. Collectively, this optimized protocol provides a reliable technical platform for the large-scale clonal propagation and biotechnological breeding of C. ovata.

Somatic embryogenesis (SE) is an indispensable biotechnological platform for plant regeneration, micropropagation and genetic modification. Members of WUSCHEL-related homeobox (WOX) transcription factor family are key regulators in SE, yet their roles in Catalpa bungei remain largely unexplored. C. bungei is a high-quality ornamental tree species endemic to China with prominent horticultural ornamental value. Here, we present the first genome-wide identification and expression profiling of the CbWOX gene family during SE in C. bungei. Fourteen CbWOX genes were identified and phylogenetically classified into three major clades. These genes are distributed across the 11 chromosomes of C. bungei, and their promoter regions are enriched with cis-regulatory elements associated with phytohormone response, stress adaptation, and growth/development. Integrated transcriptome and quantitative real-time PCR (qPCR) data indicated that CbWOX2, CbWOX5, CbWOX8, and CbWOX9 were highly expressed in embryogenic callus (EC), while CbWOX1.1 and CbWOX13 were predominantly expressed in non-embryogenic callus (NEC). Notably, only eight of the fourteen CbWOX genes were significantly expressed during SE, with distinct expression profiles across developmental stages. CbWOX4.1 and CbWOX4.2 were specifically associated with yellow-green hypocotyl callus development, while CbWOX2 and CbWOX8 were highly expressed at the EC stage. During later SE stages, CbWOX1.2, CbWUS, CbWOX5, and CbWOX13 showed significant expression at the globular embryo (GE) stage, while CbWOX1.3 was specifically upregulated at the cotyledon embryo (CE) stage. Our study provides a comprehensive genomic and transcriptomic foundation for the CbWOX family in C. bungei and reveals candidate genes with stage-specific expression during SE. These findings lay a solid basis for subsequent functional research to boost SE efficiency and advance the large-scale propagation of this precious ornamental tree.