Developmentally regulated mitochondrial biogenesis and cell death competence in maize pollen

Area of Science:

• Plant Biology
• Molecular Biology
• Genetics

Background:

• Cytoplasmic male sterility (CMS) is a maternally inherited trait causing pollen abortion, often due to chimeric mitochondrial genes.
• CMS-S in maize (Zea mays) specifically involves the collapse of immature, bi-cellular pollen.
• Understanding the role of mitochondria in CMS-S pollen development is crucial.

Purpose of the Study:

• To compare the molecular and cellular characteristics of developing CMS-S and normal (N) cytoplasm pollen.
• To elucidate the role of mitochondria in the differing developmental fates of CMS-S and N pollen.
• To identify key molecular events leading to pollen collapse in CMS-S.

Main Methods:

• Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay to detect programmed cell death (PCD).
• Mitochondria-targeted green fluorescent protein (GFP) expression to visualize mitochondrial morphology and dynamics.
• Immunoblotting to analyze the abundance of respiratory pathway proteins and alternative oxidase (AOX).

Main Results:

• CMS-S pollen exhibits chromatin and nuclear fragmentation, indicative of PCD with similarities to animal apoptosis.
• Mitochondrial morphology and association with actin filaments are disrupted in CMS-S pollen compared to N pollen.
• CMS-S pollen shows increased abundance of cytochrome respiratory pathway components and declining AOX, suggesting altered mitochondrial function and reduced protection against reactive oxygen species.

Conclusions:

• Pollen collapse in CMS-S is a programmed cell death (PCD) event.
• This PCD is associated with specific mitochondrial events, including the accumulation of respiratory proteins.
• Declining levels of protective mechanisms against mitochondrial reactive oxygen species contribute to CMS-S pollen collapse.