Year: 2018
Type: peer-review
Abstract: For the last 100 years, it has been uncontroversial to state that the plant germline is set aside late in development, but there is surprisingly little evidence to support this view.In contrast, much evolutionary theory and several recent empirical studies seem to suggest the opposite-that the germlines of some and perhaps most plants may be set aside early in development.But is this really the case?How much does it matter?How can we reconcile the new evidence with existing knowledge of plant development?And is there a way to reliably establish the timing of germline segregation in both model and nonmodel plants?Answering these questions is vital to understanding one of the most fundamental aspects of plant development and evolution. Why care?The germline is the immortal cell lineage that transmits the genome between generations.Understanding the segregation of germline and soma was a key step in our understanding of evolution [1] because once the germline is segregated, mutations that occur in somatic tissues cannot be inherited.It is typically understood that germline segregation occurs early in the development of most animals and late in the development of most plants [2][3][4][5][6][7].Indeed, late germline segregation in plants is so widely accepted [6-26] that it is common to read that plants do not have a germline at all [3,27-44] (see also S1 Data, which contains full quotes in context).While this latter statement is probably not meant to be taken literally, its prevalence illustrates that the timing of germline segregation in plants is usually assumed to be a solved problem.In this essay, I argue that the timing of germline segregation in plants is far from solved.A number of recent studies have suggested that some, and possibly most, plants possess an earlysegregating and slowly dividing germline cell lineage that bears a striking resemblance to the animal germline [12,23,45].These studies run counter to the prevailing wisdom that the plant germline is well understood and suggest instead that there is considerable uncertainty about its true nature.I start by reviewing the potential selective advantages of both early and late germline segregation in plants and outlining the differences between segregation and differentiation.I then review both the old and the new empirical evidence that bears on the nature of the plant germline.I argue that we cannot say with confidence whether the germline segregates early or late in plant development or whether the timing of germline segregation is conserved or varies among species.Nevertheless, I argue that there is strong empirical and theoretical evidence for a slowly dividing 'functional germline' in many plants, and that a functional germline might fulfill
Author: Mary Gehring
Institution: Massachusetts Institute of Technology
Language: English
Subfield: Plant Science
Domain: Life Sciences
Open Access status: green
Funder: Australian Research Council
OpenAlex ID: W4251844524