The Ethylene Biosynthesis Genes ACS2 and ACS6 Modulate Disease Severity of Verticillium dahliae

Effects of Soil Rhizobia Abundance on Interactions between a Vector, Pathogen, and Legume Plant Host

Soil rhizobia promote nitrogen fixation in legume hosts, maximizing their tolerance to different biotic stressors, plant biomass, crop growth, and yield. While the presence of soil rhizobia is considered beneficial for plants, few studies have assessed whether variation in rhizobia abundance affects the tolerance of legumes to stressors. To address this, we assessed the effects of variable soil rhizobia inoculum concentrations on interactions between a legume host (Pisum sativum), a vector insect (Acyrthosiphon pisum), and a virus (Pea enation mosaic virus, PEMV). We showed that increased rhizobia abundance reduces the inhibitory effects of PEMV on the nodule formation and root growth in 2-week-old plants. However, these trends were reversed in 4-week-old plants. Rhizobia abundance did not affect shoot growth or virus prevalence in 2- or 4-week-old plants. Our results show that rhizobia abundance may indirectly affect legume tolerance to a virus, but effects varied based on plant age. To assess the mechanisms that mediated interactions between rhizobia, plants, aphids, and PEMV, we measured the relative expression of gene transcripts related to plant defense signaling. Rhizobia concentrations did not strongly affect the expression of defense genes associated with phytohormone signaling. Our study shows that an abundance of soil rhizobia may impact a plant's ability to tolerate stressors such as vector-borne pathogens, as well as aid in developing sustainable pest and pathogen management systems for legume crops. More broadly, understanding how variable rhizobia concentrations can optimize legume-rhizobia symbiosis may enhance the productivity of legume crops.

A brassinosteroid transcriptional regulatory network participates in regulating fiber elongation in cotton

Brassinosteroids (BRs) participate in the regulation of plant growth and development through BRI1-EMS-SUPPRESSOR1 (BES1)/BRASSINAZOLE-RESISTANT1 (BZR1) family transcription factors. Cotton (Gossypium hirsutum) fibers are highly elongated single cells, and BRs play a vital role in the regulation of fiber elongation. However, the mode of action on how BR is involved in the regulation of cotton fiber elongation remains unexplored. Here, we generated GhBES1.4 over expression lines and found that overexpression of GhBES1.4 promoted fiber elongation, whereas silencing of GhBES1.4 reduced fiber length. DNA affinity purification and sequencing (DAP-seq) identified 1,531 target genes of GhBES1.4, and five recognition motifs of GhBES1.4 were identified by enrichment analysis. Combined analysis of DAP-seq and RNA-seq data of GhBES1.4-OE/RNAi provided mechanistic insights into GhBES1.4-mediated regulation of cotton fiber development. Further, with the integrated approach of GWAS, RNA-seq, and DAP-seq, we identified seven genes related to fiber elongation that were directly regulated by GhBES1.4. Of them, we showed Cytochrome P450 84A1 (GhCYP84A1) and 3-hydroxy-3-methylglutaryl-coenzyme A reductase 1 (GhHMG1) promote cotton fiber elongation. Overall, the present study established the role of GhBES1.4-mediated gene regulation and laid the foundation for further understanding the mechanism of BR participation in regulating fiber development.

Comparative Transcriptome and Interaction Protein Analysis Reveals the Mechanism of IbMPK3-Overexpressing Transgenic Sweet Potato Response to Low-Temperature Stress

The sweet potato is very sensitive to low temperature. Our previous study revealed that IbMPK3-overexpressing transgenic sweet potato (M3) plants showed stronger low-temperature stress tolerance than wild-type plants (WT). However, the mechanism of M3 plants in response to low-temperature stress is unclear. To further analyze how IbMPK3 mediates low-temperature stress in sweet potato, WT and M3 plants were exposed to low-temperature stress for 2 h and 12 h for RNA-seq analysis, whereas normal conditions were used as a control (CK). In total, 3436 and 8718 differentially expressed genes (DEGs) were identified in WT at 2 h (vs. CK) and 12 h (vs. CK) under low-temperature stress, respectively, whereas 1450 and 9291 DEGs were detected in M3 plants, respectively. Many common and unique DEGs were analyzed in WT and M3 plants. DEGs related to low temperature were involved in Ca²⁺ signaling, MAPK cascades, the reactive oxygen species (ROS) signaling pathway, hormone transduction pathway, encoding transcription factor families (bHLH, NAC, and WRKY), and downstream stress-related genes. Additionally, more upregulated genes were associated with the MAPK pathway in M3 plants during short-term low-temperature stress (CK vs. 2 h), and more upregulated genes were involved in secondary metabolic synthesis in M3 plants than in the WT during the long-time low-temperature stress treatment (CK vs. 12 h), such as fatty acid biosynthesis and elongation, glutathione metabolism, flavonoid biosynthesis, carotenoid biosynthesis, and zeatin biosynthesis. Moreover, the interaction proteins of IbMPK3 related to photosynthesis, or encoding CaM, NAC, and ribosomal proteins, were identified using yeast two-hybrid (Y2H). This study may provide a valuable resource for elucidating the sweet potato low-temperature stress resistance mechanism, as well as data to support molecular-assisted breeding with the IbMPK3 gene.

Hormone Signaling and Its Interplay With Development and Defense Responses in Verticillium-Plant Interactions

Soilborne plant pathogenic species in the fungal genus Verticillium cause destructive Verticillium wilt disease on economically important crops worldwide. Since R gene-mediated resistance is only effective against race 1 of V. dahliae, fortification of plant basal resistance along with cultural practices are essential to combat Verticillium wilts. Plant hormones involved in cell signaling impact defense responses and development, an understanding of which may provide useful solutions incorporating aspects of basal defense. In this review, we examine the current knowledge of the interplay between plant hormones, salicylic acid, jasmonic acid, ethylene, brassinosteroids, cytokinin, gibberellic acid, auxin, and nitric oxide, and the defense responses and signaling pathways that contribute to resistance and susceptibility in Verticillium-host interactions. Though we make connections where possible to non-model systems, the emphasis is placed on Arabidopsis-V. dahliae and V. longisporum interactions since much of the research on this interplay is focused on these systems. An understanding of hormone signaling in Verticillium-host interactions will help to determine the molecular basis of Verticillium wilt progression in the host and potentially provide insight on alternative approaches for disease management.