Plants

Low phosphorus (P) availability limits the growth and productivity of Chinese fir (Cunninghamia lanceolata) plantations in southern China. Melatonin (MT) regulates plant growth and stress responses, but its effects on Chinese fir under low P conditions remain unclear. A sand-culture pot experiment was conducted with two clones differing in P use efficiency, No. 36 and No. 41. Treatments comprised a normal-P control without MT and low P supply with 0, 25, 50, 100, 150, or 200 μmol L⁻¹ MT. Low P stress inhibited growth and photosynthetic performance and increased root membrane damage in both clones. Appropriate MT concentrations improved growth, photosynthetic performance, and pigment contents, modulated root antioxidant enzyme activities and protective compound accumulation, and reduced root malondialdehyde content and electrolyte leakage. Compared with the low P control without MT, 100 μmol L⁻¹ MT increased shoot biomass by 87.80% and 41.41%, root biomass by 78.13% and 67.18%, and whole-plant P accumulation by 24.75% and 90.10% in No. 36 and No. 41, respectively. At this concentration, stem and whole-plant P use efficiency increased in No. 36, whereas No. 41 showed a greater relative increase in whole-plant P accumulation. Principal component analysis identified ascorbate peroxidase (APX) activity, transpiration rate (Tr), and stomatal conductance (gs) as representative physiological response indicators. Among the concentrations tested, 100 μmol L⁻¹ MT produced the most favorable overall growth and physiological responses. These findings provide a physiological basis for further evaluation of melatonin as a treatment to improve Chinese fir seedling performance under P limitation.

Mirabilis himalaica (Edgew.) Heimerl, known as “Bazhu” in Tibetan medicine, is an endangered medicinal plant whose roots are traditionally used to treat nephritic edema, kidney stones, joint pain, and uterine cancer. Small Auxin-Up RNA (SAUR) genes regulate cell expansion and plant growth, yet they remain uncharacterized in M. himalaica. Here, we identified 42 SAUR family members (MhSAURs) from the M. himalaica genome. Phylogenetic analysis placed MhSAUR1 in a clade with AtSAUR36, a regulator of hypocotyl elongation, and MhSAUR5 with AtSAUR40/41/71/72, which regulate hypocotyl elongation and biomass. MhSAUR1 was preferentially expressed in fibrous roots and MhSAUR5 in lateral roots, and both were rapidly induced by exogenous IAA. Heterologous overexpression of MhSAUR1 and MhSAUR5 in Arabidopsis and tobacco promoted leaf and root growth and biomass accumulation. Using the tissue-culture-free CDB method, we further generated MhSAUR1-overexpressing M. himalaica plants, in which root length and root dry weight were significantly increased relative to empty-vector controls. Homologous validation of MhSAUR5 was not performed in this study. These results identify MhSAUR1 and MhSAUR5 as candidate auxin-responsive growth-promoting genes, with MhSAUR1 functionally validated in the native species, and indicate that CDB is a feasible, though currently low-efficiency, transformation route for this recalcitrant medicinal plant.

Mitogen-activated protein kinases (MAPKs) play important roles in plant stress signaling, but the contribution of MAPK group D in maize drought tolerance remains unclear. Here, we investigated MAPK group D ZmMAPK14 through phylogenetic and structural analyses, kinase activity assays, transgenic functional characterization, physiological measurements, biochemical analyses and RNA sequencing. ZmMAPK14 was classified as a group D MAPK containing the threonine-aspartate-tyrosine (TDY) motif, and drought stress significantly induced an increase in its kinase activity. ZmMAPK14-overexpressing lines exhibited higher survival rates, greater leaf relative water content, reduced detached-leaf water loss, lower membrane injury and reactive oxygen species (ROS) accumulation, and increased antioxidant enzyme activities. In contrast, ZmMAPK14-knockdown lines showed the opposite phenotypes. Transcriptome analysis identified 2005 drought-responsive genes in ZmMAPK14-overexpressing and knockdown lines. Gene Ontology (GO) enrichment analysis revealed significant enrichment of the “response to oxidative stress” term (GO:0006979) among drought-responsive genes in ZmMAPK14-overexpressing lines. This term comprised 313 differentially expressed genes (DEGs), including 13 antioxidant enzyme-encoding genes with diverse expression patterns. Collectively, these findings demonstrated that ZmMAPK14 positively regulates drought tolerance in maize by improving water status and strengthening antioxidant defense, providing a basis for further investigation of its underlying regulatory mechanisms.