The Pea Gene NA Encodesent-Kaurenoic Acid Oxidase

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Abstract
The gibberellin (GA)-deficient dwarf namutant in pea (Pisum sativum) has severely reduced internode elongation, reduced root growth, and decreased leaflet size. However, the seeds develop normally. Two genes, PsKAO1and PsKAO2, encoding cytochrome P450 monooxygenases of the subfamily CYP88A were isolated. Both PsKAO1 and PsKAO2 hadent-kaurenoic acid oxidase (KAO) activity, catalyzing the three steps of the GA biosynthetic pathway froment-kaurenoic acid to GA12 when expressed in yeast (Saccharomyces cerevisiae). In addition to the intermediates ent-7α-hydroxykaurenoic acid and GA12-aldehyde, some additional products of the pea KAO activity were detected, includingent-6α,7α-dihydroxykaurenoic acid and 7β-hydroxykaurenolide. The NA gene encodes PsKAO1, because in two independent mutant alleles, na-1 andna-2, PsKAO1 had altered sequences and the five-base deletion in PsKAO1 associated with thena-1 allele cosegregated with the dwarfna phenotype. PsKAO1 was expressed in the stem, apical bud, leaf, pod, and root, organs in which GA levels have previously been shown to be reduced in na plants.PsKAO2 was expressed only in seeds and this may explain the normal seed development and normal GA biosynthesis in seeds ofna plants.