Instability of the maize B chromosome

Area of Science:

• Genetics
• Plant Biology
• Cytogenetics

Background:

• The B (9) chromosome in maize is known for its instability, particularly during the second pollen mitosis, where nondisjunction can reach 95%.
• Instability can also occur during early kernel development, leading to recessive sectors in the endosperm or sporophyte due to the absence of dominant markers.

Purpose of the Study:

• To investigate the causes of B (9) chromosome loss in maize endosperm and sporophyte.
• To differentiate between fractional loss (single event) and multiple loss (mosaic pattern) of the B (9) chromosome.

Main Methods:

• Analysis of B (9) chromosome instability during pollen mitosis and kernel development.
• Investigation of chromosomal aberrations, including isochromosome and ring chromosome formation.
• Genetic analysis to identify factors controlling B (9) chromosome stability.

Main Results:

• Isochromosome formation, representing fractional loss, appears to be a byproduct of telocentric formation during the second pollen mitosis.
• Mosaic patterns of B (9) loss are associated with heritable instability, likely resulting from ring chromosome formation prior to the second pollen mitosis.
• A genetic factor was identified that significantly increases B (9) chromosome loss in the endosperm when a specific plant (1818-1) is used as the female parent.

Conclusions:

• The study elucidates distinct mechanisms, isochromosome and ring chromosome formation, underlying B (9) chromosome instability in maize.
• The findings highlight the complex chromosomal basis of B (9) chromosome loss during different developmental stages.
• A novel genetic factor influencing B (9) chromosome stability in the endosperm has been discovered, warranting further investigation.