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Shashank Sane (left) and his supervisor Ove Nilsson (right) after the dissertation; photo: Sonali Ranade
[2020-04-07] The genetic machinery controlling aging and seasonal growth in hybrid aspen is using at least partly the same molecular components. Shashank Sane, PhD student in Ove Nilsson’s group at UPSC, modified some of these components and characterised their function during those developmental processes. By comparing his results from hybrid aspen with findings in the annual plant thale cress, he demonstrated that the genetic components are similar but the way how the components work together differs. He successfully defended his PhD thesis today in P-O Bäckströms sal at SLU in Umeå.
Shashank Sane has focussed in his PhD thesis on two aspects of vegetative growth in hybrid aspen: the transition from a young to an adult stage and the adaptation to seasonal growth. The underlying regulation networks are very complex but uses similar components that are also involved in the regulation of flowering in thale cress. By genetically modifying three of these components in hybrid aspen, Shashank Sane demonstrated that they can interact in different ways with the other regulatory components of this network than was previously described for thale cress.
In his experiments, Shashank Sane used modified hybrid aspen that were overexpressing microRNA miR156 and others in which microRNA miR172 was inactivated. MicroRNAs are small molecular regulators of gene expression that are found in all plants and animals. MiR156 is in thale cress active in seeds and young plants and inhibits genes that induce flowering. In contrast, miR172 becomes activated with increasing age and blocks genes that repress flowering. The two microRNAs counteract each other in its action and their regulation is closely adjusted to each other.
The two differently modified hybrid aspen trees showed similar characteristics. In the second growing season when the leaves are normally getting a shorter and rounded form and become darker green, the leaves of the modified trees were still longer and lighter green, typical characteristics of young leaves. Shashank and his colleagues concluded that the modified trees need longer to pass from the young state into the adult state than the non-modified trees. They also simulated autumn conditions through shortening of the day length. The modified trees needed one week more than non-modified trees until they stopped their growth.
“We expected that these two gene modifications have similar effects on the growth of the trees as miR156 is once overactive and in the other trees, its antagonist miR172 is blocked,” says Shashank Sane. “But it was really astonishing for us to see that some of the genes that are regulated by those two microRNAs were regulated in the opposite way in hybrid aspen than in thale cress. Our suggestion is that the function of these genes has evolved differently in hybrid aspen than in thale cress, probably to adjust to the perennial growth.”
The researchers made a similar observation when studying the hybrid aspen genes that correspond to the thale cress gene GIGANTEA. In thale cress, this gene is part of a regulation network that senses the day length and regulates flowering. Shashank Sane and his colleagues focussed on the role of the poplar GIGANTEA genes for growth cessation and bud formation. Also here, they demonstrated that the network components interact in different ways to regulate the growth stop and bud set in hybrid aspen than they do during induction of flowering in thale cress.
About the public defence:
The public defence took place on Tuesday, 7th of April at SLU Umeå. The faculty opponent was Professor Miguel Blazquez from the Institute for Plant Molecular and Cellular Biology, Valencia, Spain who participated in the defence remotely. Shashank Sane's supervisor was Prof. Ove Nilsson. The defence was live broadcasted.
Title of the thesis: Molecular Regulation of Bud Phenology and Vegetative Phase Change in Populus Trees
Link to the thesis: https://pub.epsilon.slu.se/16768/
For more information, please contact:
Shashank Sane
Department of Forest Genetics and Plant Physiology
Umeå Plant Science Centre
Swedish University of Agricultural Sciences
Email:
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Several of the female scientists currently working at UPSC (photo: Anne Honsel)
[2020-02-11] Today is the International Day for Women and Girls in Science. Time to reflect on UPSC’s achievements in terms of gender equality. Since 2007, UPSC is working on improving its gender balance among its scientists and has reached now its goal of having 40-60 percent of women throughout the different career stages – from PhD students to full professors.
It all started on initiative of Vinnova and VR who funded a large project, the Berzelii Centre for Forest Biotechnology that continues now as a Vinnova Competence Centre. The funding agencies asked to analyse the gender equality within the centre and which actions were planned to improve the situation. This was when the UPSC management started to think about ways to address a gender imbalance among group leaders. Since then, the percentage of female group leaders at UPSC has increased continuously and is now at 45 percent.
“When we started to analyse the gender balance in 2007, we were pretty much balanced for PhD students, slightly imbalanced for postdocs but at the group leader positions there was a clear bias towards men that got progressively worse as you moved from assistant to associate professors and with just one full professor that was female”, says Ove Nilsson, director of UPSC. “We realized that if we could maintain the balance that we have at the PhD and postdoc level when these people move further on in their career, the imbalance would start to even out.”
That is why the UPSC management started to implement a programme to support specifically newly started group leaders. This was possible due to the funding from Vinnova and VR and the matching funding from the universities. All new group leaders received extra resources to hire e.g. PhD students and postdocs and it ensured that they had six instead of four years of funding for their own positions. The aim was to give them the good conditions to merit themselves and to allow them to establish their group.
“We did not do anything that was specifically targeted towards women”, explains Ove Nilsson. “Just by giving young researchers good starting conditions we managed to level out the gender imbalance among group leaders. The challenge now is to maintain this balance. We continue to support new group leaders with good starting packages but we also hope that now when our environment is more balanced, it becomes more attractive for all genders and like this maintains its balance.”
Special caution is set on the recruitment process. The goal is to prevent any bias but focus on recruiting the best qualified person for the respective position. The UPSC management tries to enforce this all the way from PhD students, to postdocs and group leaders. Of special help for recruiting excellent scientists and especially female scientists is of course Sweden’s family friendliness. “Many foreign scientists are not aware of the support that is offered to families with kids when they come to Sweden but after a while, they appreciate it a lot”, emphasizes Ove Nilsson.
The purpose of the International Day for Women and Girls in Science is to empower women and girls in science to achieve equality. It was established in 2005 by the United Nations General Assembly and implemented by UNESCO and UN-Women. According to UN-Women, 30 percent of researchers world-wide are women and they are still disadvantaged in their career.
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Hannele Tuominen (left) and Sacha Escamez (right) in the UPSC greenhouse (photo: Anne Honsel)
[2020-01-16] For long, it was assumed that cell death occurs mainly during animal organ growth but not in plant organs. A research group led by Hannele Tuominen from UPSC demonstrated now that the death of certain cells in the root facilitated the growth of lateral roots. These new findings hint at organ growth of plants and animals might not be so different as thought. The study was published today in the journal Current Biology.
In contrast to animals, plants are forming new organs like lateral roots continuously. These roots grow out from the main root and help to explore the soil for nutrients and give additional stability to anchor the plant in the soil. Elimination of cells plays an important role in animal development, e.g. for the formation of fingers or toes. The cells between the digits die during development to allow the establishment of the individual digits. Also in plants, developmental cell death occurs but so far it was not clear that it is needed to facilitate the emergence of lateral roots like it is shown now in the recent publication.
The researchers around Hannele Tuominen, until 2019 associate professor at Umeå University and now professor at SLU, and her postdoc Sacha Escamez used different methods to demonstrate that cell death is occurring and enables lateral roots to emerge from the main root in the plant thale cress. “We first found that genes, indicating developmental cell death, were activated in cells that are laying over those cells that form the future lateral roots”, says Hannele Tuominen. “That made us curious and we wanted to analyse this in more detail.”
The researchers used different microscopic techniques to show that those cells were actually dying. Among others, they applied dyes that stain either living cells or dead cells and fluorescent markers that are only visible at certain pH values. Important parts of the plant cells become acidic when the cell dies causing the signal from the marker to disappear.
To make the story even more thorough, the researchers used an additional approach. They analysed a thale cress mutant which is lacking a cell death regulating protein. The growth of lateral roots in this mutant was delayed. The researchers could restore the normal development genetically and also physically by using optical tweezers.
In the genetic approach, they introduced a mammalian gene, known to induce cell death, into the mutant and targeted it to only affect those cell types that they observed to die in the non-mutated plants. The lateral roots of the resulting double mutant grew normal without any delay.
In parallel, the researchers applied optical tweezers to wound cells and like this induce the death of the cell. Optical tweezers use a highly focused laser beam to manipulate microscopically small objects. “This is a very precise optical tool. We can target individual cells and wound them. Three hours after we wounded the cells, they died”, explained Sacha Escamez. “When we applied this method to the mutant whose lateral roots normally grow slower, their lateral roots grew significantly faster.”
Researchers from UPSC, from Umeå University, Israel, Germany and the United Kingdom contributed to the publication. “We started this project several years ago and are very pleased that we could now round it up with help of the expertise of all contributing authors”, pointed Hannele Tuominen out. “However, as it is often in science, this will not be the end of the story but it opens up many new questions for further studies.”
About the article:
Sacha Escamez, Domenique André, Bernadette Sztojka, Benjamin Bollhöner, Hardy Hall, Béatrice Berthet, Ute Voß, Amnon Lers, Alexis Maizel, Magnus Andersson, Malcolm Bennett and Hannele Tuominen (2020). Cell death in cells overlying lateral root primordia facilitates organ growth in Arabidopsis. Current Biology.
https://www.cell.com/current-biology/fulltext/S0960-9822(19)31580-5
For more information, please contact:
Hannele Tuominen
Department of Plant Physiology
Umeå Plant Science Centre
Umeå University
Email:
Phone: +46 90 786 9693
Twitter: @hanneletuominen
https://www.upsc.se/hannele_tuominen
Sacha Escamez
Department of Plant Physiology
Umeå Plant Science Centre
Umeå University
Email:
Twitter: @SachaEscamez
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