Practice question

GNOM encodes ARF-GEF controlling formation of COPI-independent transport vesicles that recycle PIN auxin carriers from endosomes to basal and apical plasma membrane domains. Loss-of-function gnom alleles accumulate PINs in intracellular agglomerations, abolish differential auxin maxima at embryo apex and root pole, and disrupt apical-basal axis specification. Resultant embryos display abnormal zygote division, fused collar-like cotyledons, complete loss of axial distinctions, root pole absence, and dwarf stature phenocopying chemical inhibition with NPA. Hence vesicle trafficking machinery translates biochemical hormone gradients into morphological polarity and stable tissue identities during plant embryogenesis.