Scientists at North Carolina State University have discovered a phenomenon never seen before in plants while studying molecular changes inside tree cells as wood is formed.

In research published online in Proceedings of the National Academy of Sciences the week of Aug. 20, the team found that one member of a family of proteins called transcription factors took control of a cascade of genes involved in forming wood, which includes a substance called lignin that binds fibers together and gives wood its strength.

The controller protein regulated gene expression on multiple levels, preventing abnormal or stunted plant growth. And it did so in a novel way.

The controller, a spliced variant of the SND1 family, was found in the cytoplasm outside the cell nucleus. This is abnormal, because transcription factor proteins are always in the nucleus. But when one of the four other proteins in its family group was present, the spliced variant was carried into the nucleus, where it bound to the family member, creating a new type of molecule that suppressed the expression of a cascade of genes.

“This is nothing that’s been observed before in plants,” says Dr. Vincent Chiang, co-director of NC State’s Forest Biotechnology Group with Dr. Ron Sederoff. Chiang’s research team was the first to produce a transgenic tree with reduced lignin. High lignin levels are desirable for lumber, but lignin is removed during the process of making paper or manufacturing biofuels.

Chiang, a professor in the College of Natural Resources, described the team’s finding as the long-sought path to understanding the hierarchy of gene regulation for wood formation.

Lead authors are Dr. Quanzi Li, senior research associate, who discovered the controller protein, and doctoral student Ying-Chung Lin, who carried out extensive experimental work, demonstrating with Li that the controller protein was carried into the nucleus.

The research was funded with a grant from the U.S. Department of Energy’s Office of Biological and Environmental Research.

Note to editors: An abstract of the study follows.

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“Splice variant of the SND1 transcription factor is a dominant negative of SND1 members and their regulation in Populus trichocarpa”

Published: Online the week of Aug. 20 in Proceedings of the National Academy of Sciences

Authors: Quanzi Li, Ying-Chung Lin, Ying-Hsuan Sun, Jian Song, Hao Chen, Xing-Hai Zhang, Ronald R. Sederoff, and Vincent L. Chiang. All are members of the Forest Biotechnology Group in the Department of Forestry and Environmental Resources at North Carolina State University, except for Xing-Hai Zhang, who is with the Department of Biological Sciences at Florida Atlantic University.

Abstract: Secondary Wall-Associated NAC Domain 1s (SND1s) are transcription factors (TFs) known to activate a cascade of TF and pathway genes affecting secondary cell wall biosynthesis (xylogenesis) in Arabidopsis and poplars. Elevated SND1 transcriptional activation leads to ectopic xylogenesis and stunted growth. Nothing is known about the upstream regulators of SND1. Here we report the discovery of a stem-differentiating xylem (SDX)-specific alternative SND1 splice variant, PtrSND1-A2IR, that acts as a dominant negative of SND1 transcriptional network genes in Populus trichocarpa. PtrSND1-A2IR derives from PtrSND1-A2, one of the four fully spliced PtrSND1 gene family members (PtrSND1-A1, -A2, -B1, and -B2). Each full-size PtrSND1 activates its own gene, and all four full-size members activate a common MYB gene (PtrMYB021). PtrSND1-A2IR represses the expression of its PtrSND1 member genes and PtrMYB021. Repression of the autoregulation of a TF family member by its only splice variant has not previously been reported in plants. PtrSND1-A2IR lacks DNA binding and transactivation abilities but retains dimerization capability. PtrSND1-A2IR is localized exclusively in cytoplasmic foci. In the presence of any full-size PtrSND1 member, PtrSND1-A2IR is translocated into the nucleus exclusively as a heterodimeric partner with full-size PtrSND1s. Our findings are consistent with a model in which the translocated PtrSND1-A2IR lacking DNA-binding and transactivating abilities can disrupt the function of full-size PtrSND1s, making them nonproductive through heterodimerization, and thereby modulating the SND1 transcriptional network. PtrSND1-A2IR may contribute to transcriptional homeostasis to avoid deleterious effects on xylogenesis and plant growth.

For more information, contact:
Dr. Vincent Chiang, Forest Biomaterials Group, 919/513-0098 or vincent_chiang@ncsu.edu
D’Lyn Ford, NC State News Services | 919.513.4798 or dlyn_ford@ncsu.edu

An agouti with the black palm tree’s orange fruit, which contains large seeds.

There’s no honor among thieves when it comes to rodent robbers—which turns out to be a good thing for tropical trees that depend on animals to spread their seeds.

Results of a yearlong study in Panama, published online in Proceedings of the National Academy of Sciences the week of July 16, suggest that thieving rodents helped the black palm tree survive by taking over the seed-spreading role of the mighty mastodon and other extinct elephant-like creatures that are thought to have eaten these large seeds.

Dr. Roland Kays

“The question is how this tree managed to survive for 10,000 years if its seed dispersers are extinct,” says Roland Kays, a zoologist with North Carolina State University and the North Carolina Museum of Natural Sciences. “There’s always been this mystery of how does this tree survive, and now we have a possible answer for it.”

The study showed that agoutis, rainforest rodents that hoard seeds like squirrels, repeatedly stole from their neighbors’ underground seed caches. All that pilfering moved some black palm seeds far enough from the mother tree to create favorable conditions for germination.

“We knew that these rodents would bury the seeds but we had no idea that there would be this constant digging up of the seed, moving it and  burying it, over and over again,” says Kays, a member of the Smithsonian Tropical Research Institute team. “As rodents steal the same seed many, many times, it adds up to a long-distance movement of the seed that one animal by itself could have never done.”

One seed was buried 36 times before an agouti dug it up and ate it. About 14 percent of the seeds survived until the following year.

The study, funded with a National Science Foundation grant, caught the furry thieves in the act via individual tags on agoutis, video surveillance of seed caches and tiny motion-activated transmitters attached to more than 400 seeds.

Applying such sophisticated animal tracking techniques to the plant world has the potential to improve scientists’ understanding of forest ecology and regeneration, Kays says.

“When you think about global climate change and habitats shifting, for a forest to move into new areas, trees need to have their seeds moved into new areas. This opens up a route to study how animals can help trees adjust to climate change through seed dispersal.”

Kays, a faculty member with NC State’s College of Natural Resources, was part of an international team that included scientists from Ohio State University and institutions in the Netherlands, Belgium, the United Kingdom and Germany.

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Media Contacts: 
Dr. Roland Kays, roland_kays@ncsu.edu or via Skype at roland.kays
D’Lyn Ford, News Services, 919/513-4798 or 919/480-9493 dlyn_ford@ncsu.edu

Note to editors: An abstract of the paper follows.
 
“Thieving Rodents as Substitute Dispersers of Megafaunal Seeds”
Authors: Patrick A. Jansen, Smithsonian Tropical Research Institute, Centre for Ecosystem Studies -Wageningen University, Center for Ecological and Evolutionary Studies-University of Groningen; Ben T. Hirsch, Smithsonian Tropical Research Institute, School of Environment and Natural Resources-Ohio State University; Willem-Jan Emsens, Centre for Ecosystem Studies-Wageningen University, Ecosystem Management Research Group-Department of Biology-University of Antwerp; Veronica Zamora-Gutierrez, Centre for Ecosystem Studies-Wageningen University, Department of Zoology, University of Cambridge; Martin Wikelski, Smithsonian Tropical Research Institute, Max Planck Institute for Ornithology; Roland W. Kays, Smithsonian Tropical Research Institute, North Carolina Museum of Natural Sciences, North Carolina State University

Published: Online the week of July 16, 2012, in Proceedings of the National Academy of Sciences

Abstract: The Neotropics have many plant species that seem to be adapted for seed dispersal by megafauna that went extinct in the late Pleistocene. Given the crucial importance of seed dispersal for plant persistence, it remains a mystery how these plants have survived more than 10,000 years without their mutualist dispersers. Here we present support for the hypothesis that secondary seed dispersal by scatterhoarding rodents has facilitated the persistence of these largeseeded species. We used miniature radio transmitters to track the dispersal of reputedly megafaunal seeds by Central American agoutis, which scatter-hoard seeds in shallow caches in the soil throughout the forest. We found that seeds were initially cached at mostly short distances and then quickly dug up again. However, rather than eating the recovered seeds, agoutis continued to move and recache the seeds, up to 36 times. Agoutis dispersed an estimated 35 percent of seeds for >100 m. An estimated 14 percent of the cached seeds survived to the next year, when a new fruit crop became available to the rodents. Serial video-monitoring of cached seeds revealed that the stepwise dispersal was caused by agoutis repeatedly stealing and recaching each other’s buried seeds. Although previous studies suggest that rodents are poor dispersers, we demonstrate that communities of rodents can in fact provide highly effective long-distance seed dispersal. Our findings suggest that thieving scatter-hoarding rodents could substitute for extinct megafaunal seed dispersers of tropical large-seeded trees.