Potential Involvement of Cs1-MMP in the Arrest of Sex Organ Development during Sexual Expression in Cucumber (Cucumis sativus L.)

Abstract

Monoecious cucumber (Cucumis sativus L.) produces male and female flowers on the same plant. In the early bisexual stage, all flower buds contain primordia for both stamens and pistils and sexual differences are established by the selective arrest of sexual organ primordia. Recently, the Cs1-MMP gene was isolated from a cucumber cotyledon. Cs1-MMP encodes a putative matrix metalloproteinase (MMP) and is expressed at the boundary of senescence and programmed cell death (PCD) of the cotyledon. In animals, MMPs make up a major group of enzymes that degrade the extracellular cell matrix (ECM). In cucumber flower organs, Cs1-MMP expression was analyzed in order to clarify the relationship between the arrest of sexual organs and PCD at the molecular level. In male flowers, strong Cs1-MMP expression was detected in both sepals and the area where pistil primordia became arrested. In female flowers, the highest levels of Cs1-MMP expression were observed in the sepals and the area where stamen primordia were arrested. In both male and female flowers, Cs1-MMP expression was detected from the early stage of development to anthesis. Our results suggest that Cs1-MMP plays an important role in PCD-mediated arrest of sexual organ primordia in cucumber flowers. Thus, it is possible that sex determination in cucumber requires continuous PCD to occur at the pistil or stamen primordia.