Huihui Zhang

Cadmium (Cd) is a highly toxic heavy metal that poses a serious threat to plant growth and the quality of agricultural and animal products. Therefore, elucidating the response and regulatory mechanisms of plants to Cd stress is essential for controlling the safety of agricultural and animal products at the source. In this study, we used a Cd-tolerant alfalfa cultivar, Medicago sativa ‘Zhaodong’ (ZD), and a Cd-sensitive cultivar, M. sativa ‘Zhongmu No.1’ (ZM), to investigate their differential responses to Cd stress in terms of morphology, photosynthetic function, and oxidative damage through combined physiological and RNA-Seq analyses. The results indicated that Cd stress inhibited leaf growth and photosynthetic function, and increased oxidative damage in alfalfa. The Cd-tolerant cultivar ZD exhibited greater tolerance compared to the Cd-sensitive cultivar ZM. RNA-Seq analysis revealed that the differentially expressed genes (DEGs) between the two cultivars under Cd stress were predominantly enriched in photosynthesis-related KEGG and GO pathways. Based on RNA-Seq and weighted gene co-expression network analysis (WGCNA), the MEgreen module exhibiting the highest correlation with physiological traits such as biomass and photosynthetic function was identified. The DEGs in this module were predominantly enriched in pathways related to photosynthesis and plant hormone signal transduction. Furthermore, a key gene, MsERF15, which regulates photosynthesis and ROS metabolic homeostasis in alfalfa under Cd stress, was identified. Although heterologous expression of MsERF15 significantly increased plant height in transgenic tobacco, it markedly reduced Cd stress tolerance, particularly by decreasing chlorophyll content and photochemical reaction center activity in the leaves under Cd stress, as well as elevating ROS accumulation. The potent growth-promoting effect of MsERF15 may represent a key factor contributing to its reduced Cd stress tolerance. In summary, our findings demonstrate that MsERF15 negatively regulates Cd stress tolerance in alfalfa. These results provide new insights into the adaptation mechanisms of alfalfa under Cd stress and offer a novel target for genetic improvement of Cd resistance in this important forage crop.

1 Nitrogen is an essential element for plant growth and development (Gaudinier et al. 2018). Nitrogen plays a critical role in the biosynthesis of both primary metabolites, such as proteins and nuc...

Drought is one of the primary environmental constraints limiting poplar growth. Identifying key drought‐resistance genes and their regulatory mechanisms is crucial for genetic improvement of drought tolerance in poplar. Time‐course transcriptome analysis of 84K poplar ( Populus alba × P. glandulosa ) under drought stress revealed that the ERF family is among the most responsive transcription factor families, and PagERF135A exhibited the most significant upregulation, suggesting a key regulatory role. Genome‐wide identification of the ERF family in 84K poplar identified 276 members, with expansion primarily through segmental duplication, and purifying selection dominated their evolution. PagERF135A is a nuclear‐localized transcription factor with transcriptional activation activity. Overexpression of PagERF135A reduced drought tolerance in transgenic poplars, manifested by aggravated oxidative damage, diminished osmotic adjustments, and impaired PSII and PSI activities. Integrated transcriptomic and WGCNA analyses showed that PagERF135A overexpression suppressed drought‐induced expression of soluble sugar synthesis genes in starch‐sucrose metabolism, down‐regulated brassinosteroid biosynthesis and signaling genes, and promoted catabolic genes. Thus, PagERF135A negatively regulates drought tolerance by disrupting carbon metabolic flow and brassinosteroid signaling homeostasis. Our findings provide new insights into ERF‐mediated drought response mechanisms in poplar.

GmHMGR6 coordinates a regulatory network linking nodulation, nitrogen metabolism, and photosynthesis, therebyimproving nitrogen utilization and sustaining carbon assimilation under salt stress in soybean. 3-Hydroxy-3-methylglutaryl-CoA reductase (HMGR) functions in the mevalonate pathway and is essential for plant development and stress adaptation. We identified GmHMGR6 as the most salt-responsive HMGR isoform in soybean, with predominant expression in roots. To elucidate its function in salt tolerance, we generated GmHMGR6-overexpressing hairy roots and subjected these composite plants to NaCl treatment. Physiological assays, metabolite measurements, chlorophyll fluorescence and gas-exchange analyses, together with RNA-seq of roots and leaves, were performed to characterize the GmHMGR6-dependent responses. GmHMGR6 overexpression markedly reduced salt-induced DEGs in roots relative to wild type and primarily affected nitrogen-related metabolic pathways. Leaf DEGs were enriched in photosynthesis-associated processes, including antenna proteins, electron transport, and CO₂ assimilation. GmHMGR6 also regulated key nodulation genes, thereby promoting nodule formation and enhancing nitrogen assimilation through higher ammonium levels and increased glutamine synthetase (GS) and glutamine oxoglutarate aminotransferase (GOGAT) activities. Moreover, GmHMGR6 overexpression alleviated NaCl-induced photosynthetic inhibition by maintaining photosystem function and reducing photoinhibition and oxidative damage. These findings demonstrate that GmHMGR6 enhances soybean salt tolerance through coordinated regulation of nitrogen metabolism, nodulation, and photosynthetic performance.

Drought severely impacts alfalfa yield. This study compared drought-tolerant "Zhaodong" (ZD) and sensitive "Zhongmu No.1" (ZM) cultivars. ZD maintained superior photosynthetic activity and osmotic adjustment under drought. Integrated transcriptomic and WGCNA analyses identified the JA synthesis gene MsOPR1 as a key regulator. MsOPR1 overexpression enhanced drought tolerance by protecting photosynthesis, reducing ROS, and improving osmotic adjustment. MsOPR1 promoted JA accumulation, which down-regulated MsJAZ3A and activated the transcription factor MsMYC2. MsMYC2 itself was induced by drought and JA, and its overexpression positively regulated drought resistance and JA signaling. In conclusion, JA synthesis and signaling activation, mediated by MsOPR1 and MsMYC2, are crucial for alfalfa drought adaptation, providing candidate genes and a theoretical basis for molecular breeding.

Identifying key genes involved in drought tolerance and clarifying their molecular mechanisms are crucial for breeding drought-tolerant poplar varieties. In this study, Populus alba × Populus glandulosa `84 K' was used as the experimental material to analyze its physiological and molecular responses to different levels of drought stress. Key drought-responsive genes were identified by weighted gene co-expression network analysis, and their functional roles were further validated. The results showed that drought significantly inhibited poplar growth, and both photosynthetic damage and oxidative damage in leaves increased with the severity of stress. RNA-seq analysis revealed that the differentially expressed genes in poplar leaves under drought stress were not only significantly enriched in photosynthesis and antioxidant-related pathways, but also enriched in plant hormone signal transduction and α-linolenic acid metabolism pathways, suggesting that jasmonic acid (JA) signaling plays a role in regulating the drought response of poplar. Based on the combined analysis of RNA-seq and weighted gene co-expression network analysis, PagJAZ12B was identified as a key gene. The overexpression lines of PagJAZ12B showed higher sensitivity to drought, as indicated by stronger inhibition of photosynthesis and more severe oxidative damage. In conclusion, the repressor gene PagJAZ12B in the JA signaling pathway negatively regulates drought tolerance in poplar, indicating that activation of the JA signaling pathway plays a positive role in the drought response of poplar. These findings provide important gene targets and a theoretical basis for improving drought tolerance in poplar through molecular breeding and for developing stress-resistant forestry varieties.