Crassulacean acid metabolism (CAM), one of three kinds of photosynthesis, is a water-use efficient adaptation to an arid environment. CAM is characterized by CO₂ uptake via open stomata during the nighttime and refixation CO₂ via the Calvin cycle during the daytime. Facultative CAM plants can shift the photosynthesis from C₃ to CAM and exhibit greater plasticity in CAM expression under different environments. Though leaf thickness is an important anatomical feature of CAM plants, there may be no anatomical feature changes during the C₃–CAM transition for all facultative CAM plants. The shift from C₃ photosynthesis to CAM in facultative CAM plants is accompanied by significant changes in physiology including stomata opening, CO₂ gas exchange and organic acid fluxes; the activities of many decarboxylating enzymes increase during the shift from C₃ to CAM; the molecular changes occur during the photosynthesis C₃–CAM shift involved DNA hypermethylation, transcriptional regulation, post-transcriptional regulation and protein level regulation. Recently, omics approaches were used to discover more proceedings underling the C₃–CAM transition. However, there are few reviews on the mechanisms involved in this photosynthetic shift in facultative CAM plants. In this paper, we summarize the progress in the comparative analysis of anatomical, physiological, metabolic and molecular properties of facultative CAM plants between C₃ and CAM photosynthesis. Facultative CAM plants also show the potential for sustainable food crop and biomass production. We also discuss the implications of the photosynthesis transition from C₃ to CAM on horticultural crops and address future directions for research.

Many Dendrobium species, which hold a high status and value in traditional Chinese medicine, grow on barks and rocks in the wild, often encountering harsh environments and facing droughts. However, the molecular mechanisms underlying the shift in the photosynthetic pathway induced by drought remain unclear. To address this issue, three Dendrobium species with different photosynthetic pathways were selected for sequencing and transcriptome data analysis after drought treatment. The findings included 134.43 GB of sequencing data, with numerous Differentially Expressed Genes (DEGs) exhibiting different response mechanisms under drought stress. Gene Ontology (GO)–KEGG-based enrichment analysis of DEGs revealed that metabolic pathways contributed to drought tolerance and alterations in photosynthetic pathways. Phosphoenolpyruvate Carboxylase (PEPC) was subjected to phylogenetic tree construction, sequence alignment, and domain analysis. Under drought stress, variations were observed in the PEPC gene structure and expression among different Dendrobium species; the upregulation of Dc_gene2609 expression may be caused by dof-miR-384, which resulted in the shift from C₃ photosynthesis to CAM, thereby improving drought tolerance in Dendrobium. This study revealed the expression patterns and roles of PEPC genes in enhancing plant drought tolerance and will provide an important basis for in-depth research on Dendrobium’s adaptation mechanisms in arid environments.

Many species of the Dendrobium genus are traditional Chinese herbal medicine and ornamental plants. Flower fragrance is one of the most important horticultural ornamental characters and plays a crucial role in the ecology, economy, and aesthetics of plants. However, the volatile constituents and key regulatory genes related to floral biosynthesis are poorly understood. In this experiment, the flowers from two species of Dendrobium with high-scent smells, Dendrobium moniliforme (L.) Sw. (D. moniliforme), and light-scent smells, Dendrobium nobile “H1” (D. “H1”), were selected. The aim of this study was to explore the key gene expression profiles of floral biosynthesis by combining volatile constituent determination and transcriptome analysis in two different Dendrobium species. Physiological determination results showed that 60 volatile compounds were identified in D. moniliforme and 52 volatile compounds were identified in D. ‘H1’ flowers in four flowering stages, and the full bloom stage was the most complicated stage because there were 41 and 33 volatile compounds, respectively. These compounds belong to terpenes, aromatics, fatty acids, nitrogenous compounds, ketones, alcohols, and alkanes, respectively. The components identified in the gynandrium and petals revealed that the petals were probably the most important sites affecting the release of volatiles. The relative content of terpene compounds was the highest, with 77.25% (D. moniliforme) and 50.38% (D. “H1”), respectively. Transcriptome analysis showed that differentially expressed genes (DEGs) were highly enriched in terpenoid backbone biosynthesis and that four linalool synthetase (LIS) genes were up-regulated in high-scent smell species. This study is helpful to explore the key genes of flower fragrance and provides a theoretical basis for further understanding of the regulatory molecular functions of floral synthesis and release, as well as for the cultivation of new aromatic species.

Cassava is susceptible to mites, especially Tetranychus cinnabarinus. Secondary metabolism products such as flavonoids play an important role as antimicrobial metabolites protecting plants against biotic stressors including fungal, pathogen, bacterial, and pest defense. The chalcone synthase (CHS) is the initial step of the phenylpropanoid pathway for producing flavonoids and is the gatekeeper of the pathway. Until recently, the CHS genes family has not been systematically studied in cassava. Thirty-nine CHS genes were identified from the cassava genome database. Based on phylogenetic and sequence composition analysis, these CHSs were divided into 3 subfamilies. Within the same subfamily, the gene structure and motif compositions of these CHS genes were found to be quite conserved. Duplication events, particularly segmental duplication of the cassava CHS genes, were identified as one of the main driving force of its expansion. Various cis-elements contained in the promoter might regulate the gene expression patterns of MeCHS. Protein-protein interaction (PPI) network analysis showed that MeCHS1 and MeCHS10 protein are more closely related to other family members. The expression of MeCHS genes in young leaves was higher than that in other tissues, and their expression varies even within the same tissue. Coincidentally, these CHS genes of most LAP subclasses were highly expressed in young leaves. The verified MeCHS genes showed consistent with the real-time reverse transcription quantitative PCR (RT-qPCR) and proteomic expression in protected and affected leaves respectively, indicating that these MeCHS genes play crucial roles in the response to T. cinnabarinus. This study is the first to comprehensively expatiate the information on MeCHS family members. These data will further enhance our understanding both the molecular mechanisms and the effects of CHS genes. In addition, the results will help to further clarify the effects on T. cinnabarinus and provide a theoretical basis for the potential functions of the specific CHS gene in resistance to mites and other biotic stress.

Introduction: Bletilla striata (Orchidaceae) is a valuable traditional Chinese medicinal plant prized for its dried rhizomes. However, its cultivation faces significant challenges from leaf rust disease caused by Coleosporium bletiae, which causes substantial yield losses.Methods: To investigate host resistance mechanisms, we compared rust-resistant and susceptible B. striata accessions through integrated transcriptomic and physiological analyses.Results and discussion: Phenotypic observations revealed that while both resistant and susceptible plants developed rust spores by 2 days post-inoculation (dpi), the resistant accession exhibited a significantly slower progression of spore stack formation and lesion expansion on abaxial leaf surfaces over time. Integrated transcriptomic and physiological analyses revealed that the rust-resistant material of B. striata accessions exhibited faster and stronger defense responses to pathogen infection compared to susceptible plants. These responses were characterized by significant upregulation of DEGs associated with antioxidant defense systems, secondary metabolite biosynthesis, JA, SA, and BR signaling pathways, concurrent downregulation of DEGs involved in cell wall remodeling, and calcium-mediated signaling. Furthermore, rust pathogen inoculation triggered rapid physiological responses in resistant plants, including enhanced activity of defense-related enzymes (CAT, PAL, β-1,3-glucanase, and chitinase) and early accumulation of osmolytes (soluble sugars, soluble proteins, and proline). These coordinated molecular and biochemical responses effectively restricted pathogen colonization and spread. These findings delineate the molecular basis of rust resistance in B. striata, identifying key regulatory nodes in defense pathways that could be targeted through precision breeding or genetic engineering to develop durable resistance against C. bletilla.

Flower fragrance is a crucial ornamental and economic trait of Dendrobium chrysotoxum, and the most abundant and diverse aroma-active compounds are terpenes. Terpene synthase (TPS) is the ultimate enzyme for the biosynthesis of various types of terpenes, and TPS genes were identified as the key regulators governing the spatiotemporal release of volatile terpene compounds. Until recently, the TPS gene family in D. chrysotoxum has remained largely unexplored. Our study characterizes the TPS genes in D. chrysotoxum and identifies 37 DcTPS gene family members. It helped identify the DcTPS genes, gene characteristics, the phylogeny relationship, conserved motif location, gene exon/intron structure, cis-elements in the promoter regions, protein–protein interaction (PPI) network, tissue specific expression and verification of the expression across different flowering stages and floral organs. Three highly expressed DcTPS genes were cloned, and their functions were verified using a transient expressed in tobacco leaves. Further functional verification showed that the proteins encoded by these genes were enzymes involved in monoterpene synthesis, and they were all involved in the synthesis of linalool. This study comprehensively expatiates on the TPS gene family members in D. chrysotoxum for the first time. These data will help us gain a deeper understanding of both the molecular mechanisms and the effects of the TPS genes. Furthermore, the discovery that three TPS-b genes (DcTPS 02, 10, 32) specifically drive linalool-based scent in D. chrysotoxum, will provide new insights for expanding the TPS-b subfamily in orchids and identifying the linalool synthases contributing to orchid fragrance.