CVP2-mediated IP₃ signal transduction is essential for closed venation patterns of Arabidopsis foliar organs

Francine M. Carland and Timothy Nelson

Department of Molecular, Cellular and Developmental Biology, Yale University, New Haven, CT

Vein patterns in leaves and cotyledons form in a spatially-regulated manner through the progressive recruitment of ground cells into vascular cell fate. To gain insight into venation patterning mechanisms, we have characterized the cotyledon vascular pattern 2 (cvp 2) mutants, which exhibit an increase in free vein endings and a resulting open vein network. We cloned CVP2 by a map-based cloning strategy and found that it encodes an inositol polyphosphate 5-phosphatase (5PTase). 5PTases regulate IP₃ signal transduction by hydrolyzing IP₃ and thus terminate IP₃ signaling. CVP2 gene expression is initially broad and then gradually restricted to incipient vascular cells in a number of developing organs. Consistent with the inferred enzymatic activity of CVP2, IP₃ levels are elevated in cvp2 mutants. In addition, cvp2 mutants exhibit hypersensitivity to the plant hormone abscisic acid. We propose that elevated IP₃ levels in cvp2 mutants reduce ground cell recruitment into vascular cell fate, resulting in premature vein termination, and thus in an open reticulum.