Minisymposium 1: Cell Walls

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Abs # M0103: In Search of a Molecular Houdini: Do Pectate Lyases Allow Lateral Roots to Emerge?

Presenter:	Laskowski, Marta       Contact Presenter
Authors	Laskowski, Marta  (A)   Condon, Bradford  (A)   Kajstura, Tymoteusz  (A)
Affiliations:	(A): Biology Department, Oberlin College

Lateral roots are initiated in the pericycle, deep within the parent root, and must work their way through the overlying layers of cells to reach the soil. Because openings that allow lateral roots to exit could also serve as entrance points for pathogens, maintaining tight control over cell separation is likely to be advantageous. We hypothesize that lateral root emergence is a developmentally regulated process involving selective degradation of the pectin-rich middle lamellae that surround lateral root primordia. Here we report qPCR data measuring expression levels of all 27 pectate lyase (PL) family members, and identify four that are upregulated in the root 24 h after a pulse of 10 μM IAA, a treatment that also induces lateral root formation. Expression of AtPLA2 correlates well with lateral root formation. The level of induction increases from about 4.5-fold two and a half hours after auxin treatment to about 29-fold 24 h after induction, a time at which many primordia are around emergence. Auxin induced upregulation of AtPLA2 is greatly reduced (2-fold instead of 30-fold) in slr plants, indicating that expression is downstream of IAA14. Histological stains suggest that pectin in the root primordia is predominately methylated whereas the pectin in the parent root is primarily demethylated. Because PLs preferentially cleave demethylated pectin, this could provide an explanation for why lateral roots remain largely intact while cells in the parent root separate.