The embryo MADS domain factor AGL15 acts postembryonically: Inhibition of perianth senescence and abscission via constitutive expression

AGL15 (AGAMOUS-like 15), a member of the MADS domain family of regulatory f actors, accumulates preferentially throughout the early stages of the plant life cycle. In this study, we investigated the expression pattern and poss ible roles of postembryonic accumulation of AGL15, Using a combination of r eporter genes, RNA gel blot analysis, and immunochemistry, we found that th e AGL15 protein accumulates transiently in the shoot apex in young Arabidop sis and Brassica seedlings and that promoter activity is associated with th e shoot apex and the base of leaf petioles throughout the vegetative phase. During the reproductive phase, AGL15 accumulates transiently in floral bud s. When AGL15 was expressed in Arabidopsis under the control of a strong co nstitutive promoter, we noted a striking increase in the longevity of the s epals and petals as well as delays in a selected set of age-dependent devel opmental processes, including the transition to flowering and fruit maturat ion. Although ethylene has been implicated in many of these same processes, the effects of AGL15 could be clearly distinguished from the effects of th e ethylene resistant1-1 mutation, which confers dominant insensitivity to e thylene. By comparing the petal breakstrength (the force needed to remove p etals) for flowers of different ages, we determined that ectopic AGL15 had a novel effect: the breakstrength of petals initially declined, as occurs i n the wild type, but was then maintained at an intermediate value over a pr olonged period. Abscission-associated gene expression and structural change s were also altered in the presence of ectopic AGL15.