How land was conquered by plants 480 million years ago

Washington, Feb 7 (ANI): In a new research, scientists have taken the help of mosses to understand how land was conquered by plants 480 million years ago.

The research work was done by scientists at the Washington University in St. Louis.

No would-be colonizer could have survived on dry land without the ability to deal with dehydration, a major threat for organisms accustomed to soaking in water.

Clues to how the first land plants managed to avoid drying out might be provided by bryophytes, a group that includes the mosses, many of which retain remarkable drought tolerance.

Earlier, scientists had showed that seeds depended on both the plant hormone ABA and the regulatory molecule ABI3 to survive drying.

Ralph Quatrano, senior author on the research paper, and his team set out to find the genes the ABA/ABI3 signaling pathway was controlling.

Abha Khandelwal, a postdoctoral fellow from India, identified 22 genes in wild-type moss that are upregulated and begin to churn out more protein product when the moss is treated with ABA.

These proteins, which accumulate late in seed development, are believed to protect seeds from cellular damage caused by water loss, such as the unfolding of proteins or the loss of membrane integrity.

Up until now, everything had been playing out as expected. But then something unforeseen happened.

"We treated the knockout strains with ABA to see what would happen to gene expression. We thought that none of the genes would be expressed in these strains," Quatrano said.

"To our surprise, all of them were upregulated," he added.

"To solve this puzzle, we looked at rehydration separately from dehydration. Both wild-type and knockout moss express the 22 genes during dehydration, producing messenger RNA to begin protein manufacture. The wild-type moss also expresses the genes during rehydration," he said.

"But when we rehydrated the knockout moss, all of the messenger RNA disappeared within 15 minutes," he added.

"This said to us that ABI3 either stabilizes the messenger RNA molecules whose creation is triggered by ABA, or it somehow allows messenger RNA to continue to be synthesized during rehydration," he explained.

"So the second major conclusion of the research was the timing of ABI3's role in desiccation tolerance," said Quatrano.

According to Quatrano, "Our hypothesis is that the first plants to move onto land were desiccation tolerant like P. patens and the other bryophytes, such as the hornworts and liverworts."

"As vascular plants evolved, they abandoned desiccation tolerance in favor of adaptations such as extensive root systems, waxy cuticles and stomata, that would allow them to prevent water loss rather than simply to survive it," he said. (ANI)