The late pollen-specific actins in angiosperms

Area of Science:

• Plant molecular biology
• Cell biology
• Evolutionary biology

Background:

• The Arabidopsis actin gene family exhibits diversity with vegetative and reproductive classes.
• Distinguishing highly conserved actin subclasses biochemically and cellularly is challenging.
• Understanding actin isovariant function requires specific molecular tools.

Purpose of the Study:

• To develop novel monoclonal antibodies for distinguishing Arabidopsis actin subclasses.
• To investigate the functional diversity of actin isovariants, particularly in reproductive tissues.
• To explore the evolutionary origins of specific actin epitopes.

Main Methods:

• Production of anti-actin monoclonal antibodies using Arabidopsis recombinant actins.
• Immunoblot analysis to detect actin subclass specificity in various tissues.
• Immunocytochemical studies to visualize actin filaments in pollen tubes and vegetative tissues.
• Peptide competition assays to identify the epitope responsible for antibody specificity.

Main Results:

• A novel monoclonal antibody, MAb45a, specifically recognizes two closely related reproductive actin subclasses.
• MAb45a strongly reacts with actins in mature pollen but not other Arabidopsis tissues.
• Immunocytochemistry reveals distinct actin filament localization in pollen tubes compared to vegetative tissues.
• The Asn79 epitope is crucial for MAb45a specificity and is conserved in angiosperm and advanced gymnosperm pollen.

Conclusions:

• MAb45a is a valuable tool for distinguishing reproductive actin subclasses in Arabidopsis.
• The Asn79 epitope likely emerged in an ancestor common to angiosperms and advanced gymnosperms over 220 million years ago.
• A developmental switch to reproductive actins occurs during late angiosperm pollen development, potentially for fertilization functions.