Myricaria laxiflora (Tamaricaceae) is an endangered plant that is narrowly distributed in the riparian zone of the Three Gorges, along the Yangtze River, China. Using bright-field and epifluorescence microscopy, we investigated the anatomical and histochemical features that allow this species to tolerate both submerged and terrestrial environments. The adventitious roots of Myr. laxiflora had an endodermis with Casparian bands and suberin lamellae; the cortex and hypodermal walls had lignified thickenings in the primary structure. In the mature roots, the secondary structure had cork. The apoplastic barriers in stems consisted of a lignified fiber ring and a cuticle at the young stage and cork at the mature stage. The leaves had two layers of palisade tissue, a hyaline epidermis, sunken stomata, and a thick, papillose cuticle. Aerenchyma presented in the roots and shoots. Several Myr. laxiflora structures, including aerenchyma, apoplastic barriers in the roots and shoots, were adapted to riparian habitats. In addition, shoots had typical xerophyte features, including small leaves, bilayer palisade tissues, sunken stomata, a thick, papillose cuticle, and a hyaline epidermis. Thus, our study identified several anatomical features that may permit Myr. laxiflora to thrive in the riparian zone of the Three Gorges, China.

Introduction:Adiantum nelumboides (Adiantum) is an endangered fern with a narrow distribution along the Yangtze River in China. Due to its cliff-dwelling habit, it experiences water stress conditions, which further endangers its survival. However, no information is available about its molecular responses to drought and half-waterlogging conditions.Methods: Here, we applied five and ten days of half-waterlogging stress, five days of drought stress, and rewatering after five days of drought stress, and studied the resulting metabolome profiles and transcriptome signatures of Adiantum leaves.Results and Discussion: The metabolome profiling detected 864 metabolites. The drought and half-waterlogging stress induced up-accumulation of primary and secondary metabolites including amino acids and derivatives, nucleotides and derivatives, flavonoids, alkaloids, and phenolic acid accumulation in Adiantum leaves. Whereas, rewatering the drought-stressed seedlings reversed most of these metabolic changes. Transcriptome sequencing confirmed the differential metabolite profiles, where the genes enriched in pathways associated with these metabolites showed similar expression patterns. Overall, the half-waterlogging stress for 10 days induced large-scale metabolic and transcriptomic changes compared to half-waterlogging stress for 05 days, drought stress for 05 days or rewatering for 05 days.Conclusion: This pioneering attempt provides a detailed understanding of molecular responses of Adiantum leaves to drought and half-waterlogging stresses and rewater conditions. This study also provides useful clues for the genetic improvement of Adiantum for drought/half-waterlogging stress tolerance.

The homeodomain-leucine zipper (HD-ZIP) gene family, as one of the plant-specific transcription factor families, plays an important role in regulating plant growth and development as well as in response to diverse stresses. Although it has been extensively characterized in many plants, the HD-ZIP family is not well-studied in Dendrobium officinale, a valuable ornamental and traditional Chinese medicinal herb. In this study, 37 HD-ZIP genes were identified in Dendrobium officinale (Dohdzs) through the in silico genome search method, and they were classified into four subfamilies based on phylogenetic analysis. Exon–intron structure and conserved protein domain analyses further supported the prediction with the same group sharing similar gene and protein structures. Furthermore, their expression patterns were investigated in nine various tissues and under cold stress based on RNA-seq datasets to obtain the tissue-specific and cold-responsive candidates. Finally, Dohdz5, Dohdz9, and Dohdz12 were selected to validate their expression through qRT-PCR analysis, and they displayed significantly differential expression under sudden chilling stress, suggesting they might be the key candidates underlying cold stress response. These findings will contribute to better understanding of the regulatory roles of the HD-ZIP family playing in cold stress and also will provide the vital targets for further functional studies of HD-ZIP genes in D. officinale.

Advanced techniques capable of early and non-destructive detection of the impacts of water stress on trees and estimation of the underlying photosynthetic capacities on larger scale are necessary to meet the challenges of limiting plant growth and ecological protection caused by drought. We tested influence of continuous water stress on photosynthetic traits including Leaf Chlorophyll content (LCC) and Chlorophyll Fluorescence (ChlF) and combined hyperspectral reflectance as a high-throughput approach for early and non-destructive assessment of LCC and ChlF traits in Rhamnus leptophylla trees. LCC and ChlF parameters (NPQ, Fv’/Fm’, ETR, ETRmax, Fm’, qL, qP, Y(II) were measured alongside leaf hyperspectral reflectance from Rhamnus leptophylla suffering from constant drought during water stress. Water stress caused NPQ, Fv’/Fm’, ETRmax, Fm’, qL, qP, Y(II) and ETR continuous decline throughout the entire drought period. ChlF was more sensitive to drought monitoring than LCC. The original reflectance spectra and hyperspectral vegetation indices (SVIs) showed a strong correlation with LCC and ChlF. Reflectance in 540-560nm and 750-1100nm and selected SVI such as Simple Ratio (SR)752/690 can track drought responses effectively before leaves showed drought symptoms. Multivariate Linear Regression (MLR) and three machine learning algorithms, namely Random Forest (RF), Support Vector Machine (SVM), and K-Nearest Neighbor (KNN) were employed to develop models for estimating LCC and ChlF parameters. RF provided the best estimation accuracy for LCC compared to MLR, KNN and SVM, achieving an R² value of 0.895 for all LCC samples. The canopy layer significantly influenced the estimation accuracy of LCC, with the middle layer yielding the highest R² value. RF also demonstrated superior performance compared to MLR, KNN and SVM for estimating NPQ, Fv’/Fm’, ETRmax, Fm’, qL, qP, Y(II) and ETR, achieving R² value of 0.854 for NPQ, 0.610 for Fv’/Fm’, 0.878 for ETRmax, 0.676 for Fm’, 0.604 for qL, 0.731 for qP, 0.879 for Y(II), and 0.740 for ETR. Our results indicate that photosynthetic traits combined hyperspectral reflectance can monitor the effect of drought on trees effectively with significant potential for monitoring drought over large areas.

M. laxiflora is an endangered plant that grows in the Yangtze River floodplain of China and often suffers from flooding stress. Due to the lack of a reference genome for M. laxiflora, the molecular regulatory mechanism of waterlogging stress in this plant remains unclear. In this study, we report a high-quality reference genome of M. laxiflora with a size of 1.29 Gb. A total of 23,666 gene-encoding proteins and 5457 ncRNAs were predicted in this reference genome. A comparative genome analysis revealed that 902 and 4299 gene families significantly expanded and contracted, respectively, in M. laxiflora. The expansions of the 902 gene families were significantly related to the “response to stress”, “response to abiotic stimulus”, and “response to oxygen-containing compounds” pathways. In the M. laxiflora genome, 101 MylAP2/ERF genes were identified and divided into five subgroups. Several MeJA-, ABA-, and hypoxia-responsive elements were found in the promoter regions of these MylAP2/ERF genes. According to the transcriptome data analysis, 74 MylAP2/ERF genes responded to flooding stress. Moreover, three genes (MylAP2/ERF49/78/91) that belong to the same branch as the RAP2.2 gene exhibited different expression trends under flooding stress. Our results provide valuable information on the molecular regulatory mechanism of flooding stress in M. laxiflora.

The AP2/ERF (APETALA2/ethylene-responsive element binding factor) family represents one of the largest transcription factor families in plants, playing pivotal roles in abiotic stress responses and hormone signaling pathways. Through genome-wide analysis, we identified 163 AnAP2/ERF genes in Adiantum nelumboides. Transcriptome data revealed that 12 AnAP2/ERF genes were significantly upregulated under either drought or flooding stress, with 8 genes responding to both conditions. qRT-PCR validation confirmed that all 12 selected AnAP2/ERF genes exhibited differential expression under both stress types. Notably, these genes also showed significant induction by abscisic acid (ABA), auxin (IAA), and gibberellin (GA), suggesting their potential involvement in stress responses through hormone crosstalk. This study establishes a foundation for investigating AnAP2/ERF gene functions and their molecular mechanisms in abiotic stress adaptation in A. nelumboides.