The protein complex ARP2/3 is responsible for nucleating actin, and its loss results in multiple defects in young seedlings of Arabidopsis thaliana. Sahi et al. show that plants lacking the ARP2/3 complex have defects associated with cell wall synthesis.
Mature tissues of inflorescence stems contain less cellulose and more homogalacturonan, cell walls are thinner, and lignification is altered. Stems of mutant plants have reduced basipetal auxin transport and a changed auxin influx carrier (AUX1) expression pattern. Since cell wall composition and auxin transport are functionally connected, morphogenetic defects may be explained by ARP2/3 control of cell wall synthesis and/or auxin transporters’ distribution.