Phytohormone-Based Regulation of Trichome Development

Phytohormones affect plant growth and development. Many phytohormones are involved in the initiation of trichome development, which can help prevent damage from UV radiation and insect bites and produce fragrance, flavors, and compounds used as pharmaceuticals. Phytohormones promote the participation of transcription factors in the initiation of trichome development; for example, the transcription factors HDZIP, bHLH and MYB interact and form transcriptional complexes to regulate trichome development. Jasmonic acid (JA) mediates the progression of the endoreduplication cycle to increase the number of multicellular trichomes or trichome size. Moreover, there is crosstalk between phytohormones, and some phytohormones interact with each other to affect trichome development. Several new techniques, such as the CRISPR-Cas9 system and single-cell transcriptomics, are available for investigating gene function, determining the trajectory of individual trichome cells and elucidating the regulatory network underlying trichome cell lineages. This review discusses recent advances in the modulation of trichome development by phytohormones, emphasizes the differences and similarities between phytohormones initially present in trichomes and provides suggestions for future research.

Orchestration of microtubules and the actin cytoskeleton in trichome cell shape determination by a plant-unique kinesin

Microtubules (MTs) and actin filaments (F-actin) function cooperatively to regulate plant cell morphogenesis. However, the mechanisms underlying the crosstalk between these two cytoskeletal systems, particularly in cell shape control, remain largely unknown. In this study, we show that introduction of the MyTH4-FERM tandem into KCBP (kinesin-like calmodulin-binding protein) during evolution conferred novel functions. The MyTH4 domain and the FERM domain in the N-terminal tail of KCBP physically bind to MTs and F-actin, respectively. During trichome morphogenesis, KCBP distributes in a specific cortical gradient and concentrates at the branching sites and the apexes of elongating branches, which lack MTs but have cortical F-actin. Further, live-cell imaging and genetic analyses revealed that KCBP acts as a hub integrating MTs and actin filaments to assemble the required cytoskeletal configuration for the unique, polarized diffuse growth pattern during trichome cell morphogenesis. Our findings provide significant insights into the mechanisms underlying cytoskeletal regulation of cell shape determination.

Induction of Tetraploidy to Feverfew (Tanacetum parthenium Schulz-Bip.): Morphological, Physiological, Cytological, and Phytochemical Changes

An efficient colchicine-mediated chromosome doubling of diploid feverfew followed by the morphophenological, physiological, phytochemical, and cytological changes of the obtained tetraploid plants was conducted. One-week-old seedlings of feverfew were treated with 0.05% (w/v) colchicine for 2, 4, 6, 8, and 24 h. Tetraploid plants were regenerated after 4 months, showing significant changes in stomatal size and density; sizes of seed; flower, pollen, leaf, trichome, cell, nucleus, and parthenolide content; chromosome number; ploidy level; chlorophyll content index; and quantum efficiency of photosystem II. Such characteristics of induced tetraploid feverfews can be useful in medicinal and ornamental applications, e.g., the study of flower morphogenesis, trichome differentiation, and parthenolide biosynthesis. The increase in parthenolide in tetraploids of the next generation (selfed T0 plants) showed that ploidy induction is a good breeding method for feverfew.