Transcriptome analysis of Arabidopsis wild-type and gl3-sst sim trichomes identifies four additional genes required for trichome development.

Transcriptome analyses have been performed on mature trichomes isolated from wild-type Arabidopsis leaves and on leaf trichomes isolated from the gl3-sst sim double mutant, which exhibit many attributes of immature trichomes. The mature trichome profile contained many highly expressed genes involved in cell wall synthesis, protein turnover, and abiotic stress response. The most highly expressed genes in the gl3-sst sim profile encoded ribosomal proteins and other proteins involved in translation. Comparative analyses showed that all but one of the genes encoding transcription factors previously found to be important for trichome formation, and many other trichome-important genes, were preferentially expressed in gl3-sst sim trichomes. The analysis of genes preferentially expressed in gl3-sst sim led to the identification of four additional genes required for normal trichome development. One of these was the HDG2 gene, which is a member of the HD-ZIP IV transcription factor gene family. Mutations in this gene did not alter trichome expansion, but did alter mature trichome cell walls. Mutations in BLT resulted in a loss of trichome branch formation. The relationship between blt and the phenotypically identical mutant, sti, was explored. Mutations in PEL3, which was previously shown to be required for development of the leaf cuticle, resulted in the occasional tangling of expanding trichomes. Mutations in another gene encoding a protein with an unknown function altered trichome branch formation.

The Arabidopsis SPIKE1 gene is required for normal cell shape control and tissue development.

Regulated growth and cell shape control are fundamentally important to the function of plant cells, tissues, and organs. The signal transduction cascades that control localized growth and cell shape, however, are not known. To better understand the relationship between cytoskeletal organization, organelle positioning, and regulated vesicle transport, we conducted a forward genetic screen to identify genes that regulate cytoskeletal organization in plants. Because of the distinct requirements for microtubules and actin filaments during leaf trichome development, a trichome-based morphology screen is an efficient approach to identify genes that affect cytoplasmic organization. The seedling lethal spike1 mutant was identified based on trichome, cotyledon, and leaf-shape defects. The predicted SPIKE1 protein shares amino acid identity with a large family of adapter proteins present in humans, flies, and worms that integrate extracellular signals with cytoskeletal reorganization. Both the trichome phenotype and immunolocalization data suggest that SPIKE1 also is involved in cytoskeletal reorganization. The assembly of laterally clustered foci of microtubules and polarized growth are early events in cotyledon development, and both processes are misregulated in spike1 epidermal cells.