Developmental bases for key innovations in the seed-plant microgametophyte

Area of Science:

• Evolutionary developmental biology
• Palaeobotany
• Plant reproductive biology

Background:

• The evolution of seed plants involved significant changes in the microgametophyte.
• Key innovations include altered microspore polarity, loss of sperm motility, and the development of siphonogamy (pollen tube growth).
• Understanding these shifts requires integrating data from palaeobotany and plant development.

Purpose of the Study:

• To review data from plant development and palaeobotany concerning early seed plant evolution.
• To explore the significance of microgametophyte innovations in the context of seed plant relationships.
• To connect the proximal-distal microspore polarity transition to underlying developmental changes.

Main Methods:

• Review of palaeobotanical discoveries.
• Analysis of data from interfacing fields of plant development.
• Integration of findings to understand seed plant evolution and relationships.

Main Results:

• The proximal-distal microspore polarity transition is a key evolutionary event in early seed plants.
• This transition reflects fundamental developmental shifts, including quadripartite partitioning at meiosis and asymmetric primary mitosis.
• These shifts influenced microspore polarity, germination site, aperture location, and potentially sperm motility.

Conclusions:

• The microgametophyte innovations were crucial for the early evolution of seed plants.
• The polarity transition serves as a 'fossil fingerprint' for these developmental changes.
• These evolutionary shifts had cascading effects on plant reproduction and development.