Abstract:
Endoreplication, also called endoreduplication, is a modified cell cycle in which DNA is repeatedly replicated without subsequent
cell division. Endoreplication is often associated with increased cell size and specialized cell shapes, but the mechanism
coordinating DNA content with shape and size remains obscure. Here we identify the product of the BRANCHLESS TRICHOMES
(BLT) gene, a protein of hitherto unknown function that has been conserved throughout angiosperm evolution, as a link in
coordinating cell shape and nuclear DNA content in endoreplicated Arabidopsis trichomes. Loss-of-function mutations in BLT
were found to enhance the multicellular trichome phenotype of mutants in the SIAMESE (SIM) gene, which encodes a repressor
of endoreplication. Epistasis and overexpression experiments revealed that BLT encodes a key regulator of trichome branching.
Additional experiments showed that BLT interacts both genetically and physically with STICHEL, another key regulator of
trichome branching. Although blt mutants have normal trichome DNA content, overexpression of BLT results in an additional
round of endoreplication, and blt mutants uncouple DNA content from morphogenesis in mutants with increased trichome
branching, further emphasizing its role in linking cell shape and endoreplication.
