Selective egg cell polyspermy bypasses the triploid block.

Area of Science:

• Plant genetics
• Reproductive biology
• Speciation mechanisms

Background:

• Polyploidization, an increase in genome copies, is a key driver of speciation.
• Polyspermy (fertilization by multiple sperm) has been implicated in polyploidization.
• The triploid block is a known barrier to polyploidization.

Purpose of the Study:

• To investigate the role of polyspermy in selective egg cell polyploidization.
• To determine if polyspermy can bypass the triploid block barrier.
• To assess the genetic stability and breeding potential of polyspermy-derived plants.

Main Methods:

• Utilizing a novel *sco1*-based polyspermy assay in planta.
• Analyzing genome size changes in egg and central cells after polyspermy.
• Testing the sensitivity of polyspermy-derived seeds to the triploid block suppressor *admetos*.
• Performing transcript profiling of triparental plants.

Main Results:

• Polyspermy selectively polyploidizes the egg cell, leaving the central cell unaffected.
• Polyspermy bypasses the triploid block, with most resulting seeds insensitive to *admetos*.
• Polyspermy-derived plants exhibit robustness, segregating tetraploid offspring in one generation.
• These triparental plants are comparable to triploids from interploidy crosses.

Conclusions:

• Polyspermy is a potent mechanism for inducing selective egg cell polyploidization.
• Polyspermy circumvents established postzygotic barriers like the triploid block.
• Polyspermy-derived plants offer a novel and robust route for polyploid generation in plants.
• Findings have significant implications for plant breeding strategies and understanding evolutionary processes.