A regulation for seed germination based on the physical separation of enzyme and substrate

Enhancing seed germination is a key objective of central importance to food security and for world economy. The lack of molecular understanding of seed germination, represents a fundamental gap in our ability to enhance food security across a period of rapid growing population and climate change. In this study, leads by Dr. Raquel Iglesias-Fernández, the contribution of genes encoding endo-β-mannanases (MAN) to seed germination of Brassica rapa (oilseed rape) and its close relative Sisymbrium officinale has been stablished. Transcripts of the most abundant MAN genes (MAN2, MAN5, MAN6 y MAN7) upon seed germination of these species are mainly located to micropylar endosperm in S. officinale seeds and to the radicle tip in the B. rapa embryo; however mannans have been localized to the imbibed external seed coat layer (mucilage) in both species.

This apparent discrepancy, where substrate and its hydrolytic enzyme are physically separated, suggest a movement of MAN enzymes, that are synthesized with typical signal peptides, from the embryo tissues to the mucilage layer (via apoplastic space) is necessary for the mannans to be hydrolyzed.

Figure 1 Top: Mannan polymer immunolocalization in longitudinal sections of Sisymbrium officinale seeds at 24 h of germination. Bottom: Close-up of a mucilage cell in the top image.

Original Paper:

Carrillo-Barral, N; Matilla, AJ; Rodríguez-Gacio, MdC; Iglesias-Fernández, R. 2017. "Mannans and endo-β-mannanase transcripts are located in different seed compartments during Brassicaceae germination". Planta. DOI: 10.1007/s00425-017-2815-4".