Dissecting seed genetic networks through the evolution of plant life-cycle transitions

Seeds are a critical plant product for human agriculture, but are in fact a relatively recent evolutionary innovation in a single plant lineage (the seed-bearing plants), arising from an ancestral spore-based reproductive mechanism still found in surviving seedless plant groups (mosses, liverworts, ferns etc.). How this dramatic change occurred is presently unknown and identifying genetic changes associated with it will substantially advance our fundamental understanding of how novel innovations in plant form can arise and improve our knowledge of the functions of economically-valuable genetic networks in modern seeds.

Reproductive development at first appears very different between seed-bearing plants and the various seedless plant lineages still alive today, but can be unified at two conserved transition points in their shared lifecycle- meiosis to create single haploid cells and gamete fusion to create a diploid embryo. Seeds encapsulate both of these processes but in all seedless plants they occur in two distinct and separate organs- the sporangium and the archegonium. A skeleton outline of key genes regulating seed development is known from flowering plant genetic models1 and copies of some of these genes have been found across seedless plants but their functions outside of seed-bearing plants have not been investigated.

This project aims to determine whether seed genetic networks arose from ancestral networks regulating sporangium or archegonium development. This will be achieved through a reverse genetics approach comparing the function and expression of genes between the seed-bearing genetic model Arabidopsis thaliana, the model moss Physcomitrella patens (representing early-diverging land plants) and the newly-established fern genetic model Ceratopteris richardii2,3 (belonging to the closest seedless relatives of seed-bearing plants) to map the evolutionary history of one or more candidate gene families that now regulates seed development. The analytical techniques used will include functional knock-out and ectopic expression of native homologs, functional complementation between the three plant lineages, use of fluorescent reporters of gene expression and identification of downstream and upstream regulators. Possible parallel experiments to address this question include 1) a forward-genetic mutagenesis screen to identify genes regulating reproduction in seedless plants de novo and 2) a novel synthetic biology screen expressing A. thaliana genes specific to seed tissues (seed coat, endosperm etc.) in C. richardii to compare homologies between seed and seedless reproductive tissues at the genetic level.

Project start date- October 2020.

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