Abstract
Directional growth of plant cells requires proper control of cortical microtubule organization, for which a novel Arabidopsis microtubule-localizing protein SPIRAL1 plays an important role. To better understand cellular functions of SPIRAL1, we here identified two highly homologous Arabidopsis membrane proteins (SPI1 and SPI2) that interact with SPIRAL1 in a yeast two-hybrid assay. Disruption of either SPI1 or SPI2 genes enhanced the right-handed helical growth phenotype of spiral1, whereas a double mutant of null spi1 and spi2 alleles appeared to be embryonic lethal. The SPI proteins potentially link SPIRAL1-dependent microtubule functions to endomembrane compartments.
