Inside the Exine and Perine: Understanding the Production and Evolution of Sporopollenin in Seed-Free Land Plants

Author

William Barkley Browning, Southern Illinois University CarbondaleFollow

Date of Award

12-1-2023

Degree Name

Master of Science

Department

Plant Biology

First Advisor

Geisler, Mathew

Second Advisor

Wood, Andrew

Abstract

The recalcitrant polymer sporopollenin is the primary component that contributes to the durable nature of spore and pollen walls. There has been serious interest in this enigmatic material and recent probing has unlocked the structure of this polymer. Prior to this discovery researchers utilized knockout mutants to parse out the structure of sporopollenin contributing to a biosynthetic pathway. The anther-specific chalcone synthase-like (ASCL) protein has been implicated in a key step in this pathway. Previously ASCL Knockout mutants of Physcomitrium patens have been utilized to understand the evolution of this gene. This project aims to build on these foundational studies and focus on using transmission electron microscopy (TEM) and scanning electron microscopy (SEM) techniques to ascertain a precise beginning of disruption to spore development. Along with TEM we utilize the recent surge in genomic sequencing to construct phylogenetic trees built with amino acid sequence comparison. Amino acid sequences were combined with anatomical data of various land plant taxa to construct a matrix model to correlate evolution of the ASCL protein with spore and pollen anatomy. Our findings indicate early signs of disruption prior to Spore mother cell division not previously observed. We also contribute to the growing understanding of ASCL evolution by finding novel ASCL homologs.