Sexual reproduction in animals and plants share common elements, but little was known about how the sex of plants is determined until University of Tasmania researchers discovered a gene responsible.

Dr Scott McAdam, Associate Professor Timothy Brodribb and Dr Frances Sussmilch from the School of Biological Sciences led an international collaboration involving world-leading researchers from Germany’s University of Würzburg and Purdue University, USA, to characterise a fern gene essential for the perception of a sex-determining hormone.

The research highlights the extraordinary effect that a plant hormone - abcisic acid, or ABA - which originally evolved to control sex, has had on land plant evolution and ecology over the past 450 million years.

Since the dawn of land plants, ABA has played a critical role in regulating plant responses to water availability.

The research found that the same hormone-signalling components are used in sex determination of ferns as those used for the control of seed dormancy and transpiration (the loss of water vapour through pores in the leaves) in seed plants.

The study is the culmination of three decades of genetic work with a fern species, coupled with the latest molecular and physiological techniques for gene characterisation, protein function and plant behaviour.

The breakthrough could provide a boost for Tasmania’s agriculture and forestry industries.

Dr McAdam, an Australian Research Council Discovery Early Career Researcher Award fellow, said the discovery meant scientists now understood how plants become male or female.

“In animals such as humans, X and Y chromosomes make a person male or female, but in ferns a hormonal balance in a one-day old plant sets maleness or femaleness and we previously had no idea how,” Dr McAdam said.

“What is really exciting about our discovery is that we now know of a gene that regulates sex by hormone perception and that it has done this for a very long time, at least 370 million years, from when our ancestors were still fish.”

The research shows that through the gene GAIA1, hormones are able to control the sex of plants, and that over time plants have evolved additional uses for this perception pathway.

These uses include the control of seed dormancy (essential for an even germination of crops) and the control of excessive plant water loss (essential for plants growing in dry environments).

“This gene first evolved to control sex, but it was so good at informing the plant about the environment that plants now use it for other things like seed dormancy as well as the restriction of water loss from leaves,” Dr McAdam said.

“This evolutionary change means that this gene is used by every one of our most important crop and forest species to survive during drought or on hot days.

“In 2015-16 Tasmania experienced an extreme drought, and the subsequent fires destroyed huge areas of rainforest.

“If it wasn’t for this hormone perception gene stopping the remaining plants in these forests from losing all of their water reserves, Tasmania would now be a desert.

“Understanding how these plant processes operate at a genetic level provides the critical first step towards making major improvements to drought tolerance in crop and forest species, or more ideal sex ratios in crops that produce both male and female flowers.”

Dr McAdam and Associate Professor Brodribb received funding for this research from the Australian Research Council (DE140100946 and DP140100666).​

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