Yuman Cao

Plant growth and development are intricately regulated by molecular mechanisms, with the mitogen‐activated protein kinase (MAPK) signaling cascade and its associated modules being pivotal. In this study, we identified and characterized a member of the MAPKKK family, MtMAP3Kδ6 , from Medicago truncatula . This gene, classified within the B3 subgroup of the MAPKKK family, was expressed across various tissues during plant growth. The knockout mutant of MtMAP3Kδ6 displayed dwarfism, characterized by reduced branching and smaller leaf size, whereas overexpression of MtMAP3Kδ6 in Medicago truncatula led to the converse phenotypes. Transcriptome analysis and subsequent validation in leaves from different strains showed that the knockout mutants of MtMAP3Kδ6 had decreased levels of starch and sucrose, along with diminished cell wall invertase (INV; EC 3.2.1.26) activity, whereas overexpression resulted in the opposite effects. Collectively, our findings suggest that MtMAP3Kδ6 plays a role in Medicago truncatula growth and development by positively modulating sugar metabolism. This research lays a theoretical groundwork for future studies on the role of MAPKKK in sugar metabolism and its implications for plant growth and development.

Drought has a devastating impact, presenting a formidable challenge to agricultural productivity and global food security. Among the numerous ABC transporter proteins found in plants, the ABCG transporters play a crucial role in plant responses to abiotic stress. In Medicago sativa, the function of ABCG transporters remains elusive. Here, we report that MsABCG1, a WBC‐type transporter highly conserved in legumes, is critical for the response to drought in alfalfa. MsABCG1 is localized on the plasma membrane, with the highest expression observed in roots under normal conditions, and its expression is induced by drought, NaCl and ABA signalling. In transgenic tobacco, overexpression of MsABCG1 enhanced drought tolerance, evidenced by increased osmotic regulatory substances and reduced lipid peroxidation. Additionally, drought stress resulted in reduced ABA accumulation in tobacco overexpressing MsABCG1, demonstrating that overexpression of MsABCG1 enhanced drought tolerance was not via an ABA‐dependent pathway. Furthermore, transgenic tobacco exhibited increased stomatal density and reduced stomatal aperture under drought stress, indicating that MsABCG1 has the potential to participate in stomatal regulation during drought stress. In summary, these findings suggest that MsABCG1 significantly enhances drought tolerance in plants and provides a foundation for developing efficient drought‐resistance strategies in crops.

Alfalfa, an essential forage crop known for its high yield, nutritional value, and strong adaptability, has been widely cultivated worldwide. The yield and quality of alfalfa are frequently jeopardized due to environmental degradation. Lignin, a constituent of the cell wall, enhances plant resistance to abiotic stress, which often causes osmotic stress in plant cells. However, how lignin responds to osmotic stress in leaves remains unclear. This study explored the effects of osmotic stress on lignin accumulation and the contents of intermediate metabolites involved in lignin synthesis in alfalfa leaves. Osmotic stress caused an increase in lignin accumulation and the alteration of core enzyme activities and gene expression in the phenylpropanoid pathway. We identified five hub genes (CSE, CCR, CADa, CADb, and POD) and thirty edge genes (including WRKYs, MYBs, and UBPs) by integrating transcriptome and metabolome analyses. In addition, ABA and ethylene signaling induced by osmotic stress regulated lignin biosynthesis in a contradictory way. These findings contribute to a new theoretical foundation for the breeding of high-quality and resistant alfalfa varieties.

Glycoside hydrolase family 1 (GH1) β-glucosidases (BGLUs), are encoded by a large number of genes, which participate in the development and stress response of plants, particularly under biotic and abiotic stresses through the activation of phytohormones. However, there are few studies systematically analyzing stress or hormone-responsive BGLU genes in alfalfa. In this study, a total of 179 BGLU genes of the glycoside hydrolase family 1 were identified in the genome of alfalfa, and then were classified into five distinct clusters. Sequence alignments revealed several conserved and unique motifs among these MsBGLU proteins. Many cis-acting elements related to abiotic stresses and phytohormones were identified in the promoter of some MsBGLUs. Moreover, RNA-seq and RT-qPCR analyses showed that these MsBGLU genes exhibited distinct expression patterns in response to different abiotic stress and hormonal treatments. In summary, this study suggests that MsBGLU genes play crucial roles in response to various abiotic stresses and hormonal responses, and provides candidate genes for stress tolerance breeding in alfalfa.

: Torenia fournieri Lind. is an ornamental plant, popular for its numerous flowers and variety of colors. However, its genomic evolution, as well as the genetic and metabolic basis of flower color formation, remain poorly understood. Here we report a chromosome-level reference genome of T. fournieri comprising 164.4 Mb. Phylogenetic analysis revealed the phylogenetic placement of the species, and comparative genomics analysis indicated that T. fournieri shared a whole genome duplication (WGD) event with Antirrhinum majus . Through joint transcriptomics and metabolomics analyses, we characterized the differential genes and metabolites in the anthocyanin synthesis pathway in five T. fournieri varieties. We identified many metabolites related to pelargonidin, peonidin, and naringenin in Rose (R) color samples. On the other hand, the blue (B) and blue-violet (D) color samples contained many metabolites related to petunidin, cyanidin, quercetin, and malvidin. The formation of different flower colors in T. fournieri involves multiple genes and metabolites. We analyzed the results and obtained significantly different genes and metabolites related to the biosynthesis of flavonoids and anthocyanins, which are key metabolites in the formation of different flower colors. Our T. fournieri genome data provide a basis for studying the differentiation of this species and provide a valuable model genome enabling genetic studies and genomics-assisted breeding of T. fournieri . Highlight: The genome of Torenia fournieri was reported for the first time, and the formation mechanism of different colors in Torenia fournieri flowers was analyzed by genomics, transcriptomics and metabolomics.

Adaptive changes in crops contribute to the diversity of agronomic traits, which directly or indirectly affect yield. The change of pubescence form from appressed to erect is a notable feature during soybean domestication. However, the biological significance and regulatory mechanism underlying this transformation remain largely unknown. Here, we identified a major-effect locus, PUBESCENCE FORM 1 ( PF1 ), the upstream region of Mao1 , that regulates pubescence form in soybean. The insertion of a Ty3/ Gypsy retrotransposon in PF1 can recruit the transcription factor GAGA-binding protein to a GA-rich region, which up-regulates Mao1 expression, underpinning soybean pubescence evolution. Interestingly, the proportion of improved cultivars with erect pubescence increases gradually with increasing latitude, and erect-pubescence cultivars have a higher yield possibly through a higher photosynthetic rate and photosynthetic stability. These findings open an avenue for molecular breeding through either natural introgression or genome editing toward yield improvement and productivity.

Drought, bringing the risks of agricultural production losses, is becoming a globally environmental stress. Previous results suggested that legumes with nodules exhibited superior drought tolerance compared with the non-nodule group. To investigate the molecular mechanism of rhizobium symbiosis impacting drought tolerance, transcriptome and sRNAome sequencing were performed to identify the potential mRNA–miRNA–ncRNA dynamic network. Our results revealed that seedlings with active nodules exhibited enhanced drought tolerance by reserving energy, synthesizing N-glycans, and medicating systemic acquired resistance due to the early effects of symbiotic nitrogen fixation (SNF) triggered in contrast to the drought susceptible with inactive nodules. The improved drought tolerance might be involved in the decreased expression levels of miRNA such as mtr_miR169l-5p, mtr_miR398b, and mtr_miR398c and its target genes in seedlings with active nodules. Based on the negative expression pattern between miRNA and its target genes, we constructed an mRNA–miR169l–ncRNA ceRNA network. During severe drought stress, the lncRNA alternative splicings TCONS_00049507 and TCONS_00049510 competitively interacted with mtr_miR169l-5p, which upregulated the expression of NUCLEAR FACTOR-Y (NF-Y) transcription factor subfamily NF-YA genes MtNF-YA2 and MtNF-YA3 to regulate their downstream drought-response genes. Our results emphasized the importance of SNF plants affecting drought tolerance. In conclusion, our work provides insight into ceRNA involvement in rhizobium symbiosis contributing to drought tolerance and provides molecular evidence for future study.

(1) Background: Alfalfa is an important legume forage throughout the world. Although alfalfa is considered moderately tolerant to salinity, its production and nitrogen-fixing activity are greatly limited by salt stress. (2) Methods: We examined the physiological changes and proteomic profiles of alfalfa with active nodules (NA) and without nodules (NN) under NaCl treatment. (3) Results: Our data suggested that NA roots showed upregulation of the pathways of abiotic and biotic stress responses (e.g., heat shock proteins and pathogenesis-related proteins), antioxidant enzyme synthesis, protein synthesis and degradation, cell wall degradation and modification, acid phosphatases, and porin transport when compared with NN plants under salt stress conditions. NA roots also upregulated the processes or proteins of lipid metabolism, heat shock proteins, protein degradation and folding, and cell cytoskeleton, downregulated the DNA and protein synthesis process, and vacuolar H⁺-ATPase proteins under salt stress. Besides, NA roots displayed a net H⁺ influx and low level of K⁺ efflux under salt stress, which may enhance the salt tolerance of NA plants. (4) Conclusions: The rhizobium symbiosis conferred the host plant salt tolerance by regulating a series of physiological processes to enhance stress response, improve antioxidant ability and energy use efficiency, and maintain ion homeostasis.