The homeodomain-leucine zipper (HD-ZIP) transcription factors, representing one of the largest plant-specific superfamilies, play important roles in the response to various abiotic stresses. However, the functional roles of HD-ZIPs in abiotic stress tolerance and the underlying mechanisms remain relatively limited in Miscanthus sinensis. In this study, we isolated an HD-ZIP TF gene, MsHDZ23, from Miscanthus and ectopically expressed it in Arabidopsis. Transcriptome and promoter analyses revealed that MsHDZ23 responded to salt, alkali, and drought treatments. The overexpression (OE) of MsHDZ23 in Arabidopsis conferred higher tolerance to salt and alkali stresses compared to wild-type (WT) plants. Moreover, MsHDZ23 was able to restore the hb7 mutant, the ortholog of MsHDZ23 in Arabidopsis, to the WT phenotype. Furthermore, MsHDZ23-OE lines exhibited significantly enhanced drought stress tolerance, as evidenced by higher survival rates and lower water loss rates compared to WT. The improved drought tolerance may be attributed to the significantly smaller stomatal aperture in MsHDZ23-OE lines compared to WT. Furthermore, the accumulation of the malondialdehyde (MDA) under abiotic stresses was significantly decreased, accompanied by dramatically enhanced activities in several antioxidant enzymes, including superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) in the transgenic plants. Collectively, these results demonstrate that MsHDZ23 functions as a multifunctional transcription factor in enhancing plant resistance to abiotic stresses.

Rhododendron hainanense Merr. is a tropical flowering shrub valued for its strong orna-mental and medicinal properties; however, its horticultural application is limited by its susceptibility to waterlogging disasters. The AP2/ERF transcription factor family plays crucial roles in plant growth, development, and responses to biotic and abiotic stresses; however, its regulatory mechanism in response to waterlogging stress remains unclear. This study conducted a genome-wide analysis of the AP2/ERF transcription factor family in R. hainanense, identifying 142 RhAP2/ERFs genes distributed across 13 chromosomes and classified into five subfamilies. Conserved motif analysis confirmed the characteristic AP2 domain structure. Gene duplication events revealed 16 segmental duplication pairs, indicating a potential role in adaptive evolution. Cis-element and protein interaction analyses suggested involvement in abiotic stress responses. Transcriptome and qRT-PCR results under waterlogging stress showed significant up-regulation of RhERF9 and RhERF95, with RhERF9 expression increasing 130-fold after 3 days, implying a positive regulatory role for the RhERF9 protein in early waterlogging response. Tissue-specific expression highlighted RhERF9’s strong induction in roots, associated with aerenchyma formation and hypoxia adaptation. The identified candidate AP2/ERF genes in R. hainanense play important roles in abiotic stress resistance and lay a foundation for future applications in breeding and horticulture.

Heat stress severely impairs normal plant growth and yield, which significantly limits the horticultural and productive application of most Rhododendron species. In contrast, Rhododendron hainanense exhibits considerable heat tolerance due to its unique growing environment; however, the molecular mechanisms underlying its response to heat stress remain poorly understood. In this study, R. hainanense plants were subjected to heat stress treatment. Combined transcriptomic and metabolomic analyses identified 5454 differentially expressed genes and 152 differential metabolites. The results demonstrated that heat stress significantly induced the accumulation of flavonoids in R. hainanense. Notably, derivatives of myricetin, quercetin, and kaempferol were abundantly accumulated, suggesting their potential role in aiding plant defense against heat stress. The significant up-regulation of specific Rh4CL and RhFLS genes under high-temperature stress, coupled with the substantial accumulation of their flavonoid products (myricetin, quercetin, and kaempferol), indicates a potential role for these metabolites in the thermotolerance of Rhododendron hainanense. These findings provide novel insights into the heat stress response and flavonoid biosynthesis regulation in R. hainanense, highlighting the critical role of flavonoids in plant adaptation to heat stress. This study offers valuable references for the genetic improvement of Rhododendron cultivars with high stress resistance.