Transcriptomic analysis reveals key early events of narciclasine signaling in Arabidopsis root apex

PLDδ, auxin, and H2O2 mediated the allelopathic effect of cycloastragenol on root growth in Arabidopsis

Cycloastragenol (CAG) is a tetra-cyclic triterpenoid allelochemical. It has been widely studied in animals but rarely in plants. Here, we reported that a model allelochemical CAG inhibited primary root elongation of Arabidopsis by reducing the sizes of both the meristem and elongation zones. Phospholipase Dδ(PLDδ), hydrogen peroxide (H₂O₂), and auxin affected this process. After treatment with CAG, the expression of PLDδ and the activity of the Phospholipase D(PLD) enzyme increased in WT. Mutants analysis demonstrated that PLDδ negatively regulated the primary root elongation by CAG treatment. CAG treatment stimulated the accumulation of H₂O₂ in roots. The production of H₂O₂ was derived from cell wall peroxidase. Mutants analysis showed that PLDδ positively regulated the production of H₂O₂ by CAG treatment. CAG also decreased auxin content in the root tip by affecting the expression of auxin synthesis-related genes. PLDδ was involved in the auxin reduction mediated by CAG, but H₂O₂ did not participate in this process. In conclusion, PLDδ, auxin, and H₂O₂ mediated the inhibition of primary root growth by CAG in Arabidopsis.

The Phytotoxin Myrigalone A Triggers a Phased Detoxification Programme and Inhibits Lepidium sativum Seed Germination via Multiple Mechanisms including Interference with Auxin Homeostasis

Molecular responses of plants to natural phytotoxins comprise more general and compound-specific mechanisms. How phytotoxic chalcones and other flavonoids inhibit seedling growth was widely studied, but how they interfere with seed germination is largely unknown. The dihydrochalcone and putative allelochemical myrigalone A (MyA) inhibits seed germination and seedling growth. Transcriptome (RNAseq) and hormone analyses of Lepidium sativum seed responses to MyA were compared to other bioactive and inactive compounds. MyA treatment of imbibed seeds triggered the phased induction of a detoxification programme, altered gibberellin, cis-(+)-12-oxophytodienoic acid and jasmonate metabolism, and affected the expression of hormone transporter genes. The MyA-mediated inhibition involved interference with the antioxidant system, oxidative signalling, aquaporins and water uptake, but not uncoupling of oxidative phosphorylation or p-hydroxyphenylpyruvate dioxygenase expression/activity. MyA specifically affected the expression of auxin-related signalling genes, and various transporter genes, including for auxin transport (PIN7, ABCG37, ABCG4, WAT1). Responses to auxin-specific inhibitors further supported the conclusion that MyA interferes with auxin homeostasis during seed germination. Comparative analysis of MyA and other phytotoxins revealed differences in the specific regulatory mechanisms and auxin transporter genes targeted to interfere with auxin homestasis. We conclude that MyA exerts its phytotoxic activity by multiple auxin-dependent and independent molecular mechanisms.

Transcriptomic Time-Series Analyses of Gene Expression Profile During Zygotic Embryo Development in Picea mongolica

Zygotic embryogenesis is a critical process during seed development in gymnosperms. However, knowledge on the genome-wide transcriptional activation that guides this process in conifers is limited, especially in Picea mongolica. This tree species is endemic to semiarid habitats of Inner Mongolia in China. To extend what is known about the molecular events underpinning its zygotic embryogenesis, comparative transcriptomic analyses of gene expression in zygotic embryos were performed by RNA sequencing in P. mongolica. Our results showed that most changes in transcript levels occurred in the early embryonic pattering determination and formation of mature embryos. Transcripts related to embryogenic competence, cell division pattern, hormones, and stress response genes were identified during embryogenesis. Auxin is essential for early embryo patterning and pre-cotyledon embryonic formation. However, ABA is a major regulator of embryo maturation. Moreover, we found that methylation-related gene expression is associated with activation of early-stage embryos, late embryogenesis abundant proteins, and storage/energy-related genes with late and mature embryos. Furthermore, network analysis revealed stage-specific and multistage gene expression clusters during embryogenesis. WOX, MYB, AP2, and HLH transcription factors seem more relevant to embryogenesis in different stages. Our results provide large-scale and comprehensive transcriptome data for embryo development in P. mongolica. These data will lay a foundation for the protection and utilization of P. mongolica resources.

A Transcriptome Analysis Revealing the New Insight of Green Light on Tomato Plant Growth and Drought Stress Tolerance

Light plays a pivotal role in plant growth, development, and stress responses. Green light has been reported to enhance plant drought tolerance via stomatal regulation. However, the mechanisms of green light-induced drought tolerance in plants remain elusive. To uncover those mechanisms, we investigated the molecular responses of tomato plants under monochromatic red, blue, and green light spectrum with drought and well-water conditions using a comparative transcriptomic approach. The results showed that compared with monochromatic red and blue light treated plants, green light alleviated the drought-induced inhibition of plant growth and photosynthetic capacity, and induced lower stomatal aperture and higher ABA accumulation in tomato leaves after 9 days of drought stress. A total of 3,850 differentially expressed genes (DEGs) was identified in tomato leaves through pairwise comparisons. Functional annotations revealed that those DEGs responses to green light under drought stress were enriched in plant hormone signal transduction, phototransduction, and calcium signaling pathway. The DEGs involved in ABA synthesis and ABA signal transduction both participated in the green light-induced drought tolerance of tomato plants. Compared with ABA signal transduction, more DEGs related to ABA synthesis were detected under different light spectral treatments. The bZIP transcription factor- HY5 was found to play a vital role in green light-induced drought responses. Furthermore, other transcription factors, including WRKY46 and WRKY81 might participate in the regulation of stomatal aperture and ABA accumulation under green light. Taken together, the results of this study might expand our understanding of green light-modulated tomato drought tolerance via regulating ABA accumulation and stomatal aperture.

Amaryllidaceae andSceletiumalkaloids

Recent progress on the isolation, identification, biological activity and synthetic studies of Amaryllidaceae alkaloids, as well as the structurally close alkaloids from theSceletiumgenus, published from July 2015 to June 2017 are reviewed.