Origin of complementary incompatibility systems in flowering plants.

Area of Science:

• Plant reproductive biology
• Evolutionary genetics
• Population genetics

Background:

• The complementary incompatibility system involves co-operative control of S specificity by multiple S genes.
• Its evolutionary origin and significance, particularly whether it's a primary or secondary development, remain debated.
• Previous hypotheses suggest a single, early polygenic origin in angiosperms.

Purpose of the Study:

• To propose an alternative hypothesis for the origin of complementary incompatibility.
• To explore the evolutionary pathways leading to complex self-incompatibility systems.
• To understand the factors driving the development of intergenic interactions in plant reproduction.

Main Methods:

• Review and synthesis of existing hypotheses on self-incompatibility evolution.
• Development of a novel hypothesis based on secondary evolution.
• Comparative analysis of potential evolutionary trajectories.

Main Results:

• An alternative hypothesis suggests complementary incompatibility evolved secondarily and polyphyletically.
• This secondary evolution occurred after the breakdown of ancestral one-locus gametophytic systems.
• Re-evolution of self-incompatibility via introgression facilitated the exclusion of allelic interactions.

Conclusions:

• Complementary incompatibility likely arose multiple times independently in angiosperm evolution.
• The breakdown and re-establishment of self-incompatibility are key processes.
• This polyphyletic origin explains the scattered distribution of such systems across different plant lineages.