Roles of theUniGene in Shoot and Leaf Development of Pea (Pisum sativum): Phenotypic Characterization and Leaf Development in theunianduni‐tacMutants

Abstract

A number of single‐gene, recessive mutations have been described in Pisum sativum L. that alter the form of the normal pinnately compound leaf and that show promise in elucidating genetic mechanisms of leaf development. Two recessive mutant alleles are known for the Unifoliata gene (the putative Lfy/Flo orthologue): uni and uni‐tac (tendrilled acacia). To better understand the role of Uni in pea, we made observations on shoot development, leaf development, and in situ expression of Uni mRNA in these two mutants in comparison to wild‐type plants. Although uni plants have abnormal, sterile flowers, those of uni‐tac are usually normal and fertile. The uni and uni‐tac plants produce more leaves and flower later than wild type, especially under long days. Some shoot features that are altered under long days are unaffected in uni plants, indicating that Uni may play a role in some photoperiodic responses. Adult uni leaves exceed one lateral leaflet pair only under short days, whereas uni‐tac leaves typically possess two to three lateral leaflet pairs and one lateral tendril pair. Fusions between the ultimate lateral pinnae and the terminal leaflet are common in both mutants. Pinnae are initiated in an acropetal sequence over five plastochrons (P) for wild type, four for uni‐tac, and three for uni. Lateral leaflet initiation and expansion occur earlier on wild‐type leaves than on the mutants. Uni mRNA is expressed in the tips of juvenile leaf primordia through P4 in wild type, through P3 in uni‐tac, and through P2 in uni. Ectopic expression also occurs in the shoot apical meristem of the mutants. We conclude that the Uni gene affects leaf development in pea by prolonging leaf tip growth and the period of pinna initiation and by delaying leaf tip differentiation. Therefore, it allows larger and more complex leaves to be produced by altering the timing of developmental events.