Vascular meristems, though less well known than their flashier sister the apical meristem, have perhaps the bigger job; they produce most of the biomass that makes up plant stems and tree trunks. The vascular meristems also produce the phloem and xylem responsible for the transportation of nutrients throughout the plant. It is the seasonal changes in growth rates from these vascular meristems that give rise to the rings observed in cross-sections of woody trees. Fisher and Turner have identified a mutation in Arabidopsis Landsberg erecta that affects the organization of those tissues arising from the vascular meristem. In phloem intercalated with xylem (pxy) mutant plants, the phloem and xylem tissues are not as neatly separated as they are supposed to be, and the cell divisions are not as coordinated as usual. The vessels are irregular in shape and trajectory, and the mature plant is much shorter than the wild type. The protein encoded by PXY has sequence features that resemble those of receptor kinases, and PXY is expressed in leaves, roots, and stems. The authors speculate that PXY may be involved in determining the correct orientation of the cell division plane. -- PJH
Curr. Biol. 17, 1061 (2007).
