Abstract
Plant trichomes originate from epidermal cell, forming protective structure from abiotic and biotic stresses. Different from the unicellular trichome in Arabidopsis, tomato trichomes are multicellular structure and can be classified into seven different types based on cell number, shape and the presence of glandular cells. Despite the importance of tomato trichomes in insect resistance, our understanding of the tomato trichome morphogenesis remains elusive. In this study, we quantitatively analyzed morphological traits of trichomes in tomato and further performed live imaging of cytoskeletons in stably transformed lines with actin and microtubule markers. At different developmental stages, two types of cytoskeletons exhibited distinct patterns in different trichome cells, ranging from transverse, spiral to longitudinal. This gradual transition of actin filament angle from basal to top cells could correlate with the spatial expansion mode in different cells. Further genetic screen for aberrant trichome morphology led to the discovery of a number of independent mutations in SCAR/WAVE and ARP2/3 complex, which resulted in actin bundling and distorted trichomes. Disruption of microtubules caused isotropic expansion while abolished actin filaments entirely inhibited axial extension of trichomes, indicating that microtubules and actin filaments may control distinct aspects of trichome cell expansion. Our results shed light on the roles of cytoskeletons in the formation of multicellular structure of tomato trichomes.
Highlights
Plant morphogenesis relies on tightly controlled cell division and cell expansion [1, 2]
We examined multicellular trichome morphology by combining cellular biology approaches and genetic mutants
We found critical roles for of the organization of actin filaments and microtubules in forming multicellular structure of tomato trichomes
Summary
Plant morphogenesis relies on tightly controlled cell division and cell expansion [1, 2]. A number of multi-cellular organs including Arabidopsis roots and pavement cells had been used as the model system to study coordinated morphogenesis [3, 4]. Trichomes, originating from epidermis protrude from the epidermal surface, form an appending structure which is an ideally simple system for studying the morphogenesis regulation. In Arabidopsis, the trichome is a unicellular structure with three or four branches. Tomato trichomes are all multicellular and generally composed of basal, stalk, and glandular head cells (only in some types) [7]. Tomato trichomes provide an optimal simple model system for studying cell division and cell expansion within a multi-cellular structure
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