Seed mucilage evolution: diverse molecular mechanisms generate versatile
ecological functions for particular environments
Abstract
The polysaccharidic mucilage is a widespread plant trait with diverse
features, often present around plant structures in contact with the
environment, providing numerous functions including protection and
adhesion. In myxodiasporous species, a mucilage is released upon the
imbibition of the seed (myxospermy) or the fruit (myxocarpy), and
therefore can play roles in the early seedling stages. It is unclear
whether myxodiaspory has one or multiple evolutionary origins and why it
disappeared in several species. Here, we summarize the recent advances
on (i) the mucilage and mucilage secretory cell diversity, (ii) the
evolution of the molecular actors involved in myxospermy underlying the
observed inter- and intra-species natural diversity and (iii) the
recently identified ecological functions. At the intra-species level, a
high polymorphism was detected for a few genes in relation to the
observed morphological diversity. Well characterized transcriptions
factors interact in master regulatory complexes to balance carbon
partitioning in Arabidopsis thaliana seeds. These transcription factors
were sequentially recruited during seed plant evolution to control
diverse traits including myxospermy, and their functions in seeds seem
to be conserved across Rosids. Historically, the ecological functions of
seed mucilage were mostly related to germination and seed dissemination
but recently some exosystemic functions were uncovered such as soil
micro-organism control and plant establishment support.