Genetic regulation of vascular tissue patterning in Arabidopsis

Plants transport water and nutrients through a complex vascular network com prised of interconnected, specialized cell types organized in discrete bund les. To identify genetic determinants of vascular tissue patterning, we con ducted a screen for mutants with altered vascular bundle organization in Ar abidopsis cotyledons, Mutations in two genes, CVP1 and CVP2 (for (c) under bar otyledon (v) under bar ascular (p) under bar attern), specifically disr upt the normal pattern of vascular bundles in cotyledons, mature leaves, an d inflorescence stems. The spatial distribution of the procambium, the prec ursor to mature vascular tissue, is altered in cvp1 and cvp2 embryos, sugge sting that CVP1 and CVP2 act at a very early step in vascular patterning, S imilarly, in developing stems of cvp1 and leaves of cvp2 the pattern of vas cular differentiation is defective, but the maturation of individual vascul ar cells appears to be normal. There are no discernible alterations in cell morphology in cvp2 mutants. In contrast, cvp1 mutants are defective in dir ectional orientation of the provascular strand, resulting in a failure to e stablish uniformly aligned vascular cells, and they also show a reduction i n vascular cell elongation. Neither cvp1 nor cvp2 mutants displayed altered auxin perception, biosynthesis, or transport, suggesting that auxin metabo lism is not generally affected in these mutants.