Progress 10/01/19 to 09/30/20
Outputs
Target Audience:During the period of review I have collaborated with Dr. Laura Marek, the USDA-ARS curator for oilseed crops, to identify floral phenotypes associated with either self- or cross-pollination in diverse sunflower genotypes. I am also developing CRISPR genome editing technologies for sunflower in a collaborative project funded by SYNGENTA. Finally, I am continuing my role as scientific advisor for a citizen science program investigating growth of sunflower plants in diverse locales. Changes/Problems:Due to the COVID-19 pandemic, our access to research facilities have been greatly curtailed and are still in the process of being ramped-up to normal levels. This has led to unavoidable delays in our research plans. However, as university policies and county health ordinances allow it, we will increase our research efforts. Also due to the pandemic, a number of scientific meetings and other outreach opportunities were cancelled this year. I anticipate that as vaccines become widely available these activities will resume. What opportunities for training and professional development has the project provided?During the period of review, I been involved in training one postdoc (C. Marshall), four graduate students (C. Baker, C. Brooks, V. Thompson, and H. Zhang) and 8 undergraduates. One undergraduate (F. Moore) was recruited via the auspices of the Plant Agricultural Biology Graduate Admissions Pathways Program, a partnership that provides students from Fort Valley State University and Tuskegee University with summer research at UC Davis. I take the mentoring of trainees seriously, especially for postdoctoral scholars who will soon be looking for independent positions. I meet on a weekly basis with the graduate students and post-docs working on this project to review not only short-term project goals but also longer-term strategic goals and their career objectives. These meeting are a forum to discuss progress on the project, future directions, mentoring issues and solutions, data analysis, manuscript writing, and career planning. All lab members participate in a weekly group meeting (now held via Zoom due to the pandemic). Participants present their research progress and lead discussions on recently published papers relevant to our research goals. I provide trainees with constructive criticism after their research presentations for more effective communication. In addition, trainees working with sunflower engage in once-monthly meeting with the labs of Ben Blackman (UC Berkeley), Jessica Barb (University of Georgia), and Laura Marek (USDA-ARS and Iowa State) to discuss methodologies, experimental plans, and new findings. Four undergraduate researchers participated in an informal bioinformatics course hosted by lab graduate students to introduce them to the R statistical language and environment ("Rundergrad Club"). This has provided an excellent foundation for their subsequent analysis and plotting of data they are generating as part of this project. Four undergraduate researchers presented their findings in spring of 2020 at the UC Davis Undergraduate Research Conference. This provided them with a valuable opportunity to reflect on how their results connect to other research efforts in the lab and to hone their science communication skills. Similarly, three graduate students and a post-doc participated in the 2020 American Society for Plant Biology meeting, Plant Biology 2020, Worldwide Summit. They presented their research results at this well-attended, highly international meeting. I both attended the meeting and served on the program committee that planned in. In this capacity, I helped increase diversity at the meeting by selecting early career researchers to act as symposia session chairs and promoting the selection of members of groups underrepresented in biology at speakers in concurrent symposia. I also presented lab research results at two international symposia, "Frontiers in Plant Environmental Response Research (held in Nagoya, Japan, in November 2019), and the 2020 Society for Research on Biological Rhythms meeting (held via online in June, 2020). How have the results been disseminated to communities of interest?We are working to communicate our findings with our target audience in different ways. First, I frequently present the lab's work to other scientists in invited seminars at international meetings and departmental seminar series. During the period of review, I reported findings from our project in invited talks at the "Frontiers in Plant Environmental Response" symposium in Nagoya, Japan and at the 2020 Society for Research on Biological Rhythms biennial meeting (virtual). I also participated in the 2020 International Chronobiology Summer School (virtual) to help broaden understanding of the importance of circadian rhythms for agronomic traits outside the field of plant biology. Three graduate students and a post-doc also presented their research findings in the 2020 American Society for Plant Biology meeting, Plant Biology 2020, Worldwide Summit. I organize monthly sunflower project meetings with the labs of Ben Blackman (UC Berkeley), Jessica Barb (University of Georgia), and Laura Marek (USDA-ARS and Iowa State). An important ongoing topic is how to best coordinate experimental efforts so as to provide Dr. Marek, oilseed curator for USDA-ARS, with useful phenotypic data on traits important for reproductive success in diverse genotypes of domesticated sunflower. I am also assisting the labs of Anne Britt and Neelima Sinha (UC Davis) with their Syngenta-funded project to develop techniques for CRISPR-mediated sunflower genome editing. We have shared our protocols for transient transformation of sunflower with the Britt and Sinha labs and are collaborating with them on their sunflower experiments. Finally, I have also served as a scientific consultant for the past four years to Mr. Peter Morgan, who is leading a plant biology-focused citizen science effort in the United Kingdom and who frequently requests her advice on experimental design. What do you plan to do during the next reporting period to accomplish the goals?As part of our effort to characterize how environmental and internal cues affect floral organ growth to promote either outcrossing or selfing, we plan to: 1. investigate a role for diffusible factors in the promotion of late-stage floral development in sunflower To help define molecular pathways controlling the timing of important plant traits in the field, we plan to: 1. initiate transcriptome experiments to identify growth pathways that regulate the appropriate timing of pollen presentation in sunflower 2. integrate transcriptome data previously generated from heliotropic sunflowers with our recently-collected phosphoproteomic data to better understand specific mechanisms regulating daily solar tracking movements In our studies on the molecular nature of the plant circadian clock itself and how it controls diverse plant growth pathways, we plan to: 1. use molecular genetic approaches to define the portions of XCT protein important for RNA processing, acute response to DNA damaging treatment, and the regulation of activity of a core clock transcription factor complex 2. use molecular genetic approaches to determine which biological pathways are responsible for altered circadian clock function in XCT mutants
Impacts
What was accomplished under these goals?
Since plants are rooted in place, they have developed a wide range of ways to respond to, and even anticipate, changes in their environment. Like most other organisms, plants use internal biological timekeepers to anticipate environmental challenges that occur on a daily basis. These timekeepers, called circadian oscillators, regulate key processes such as photosynthesis, growth, responses to various stresses, and flowering time. A functional circadian clock provides plants with a growth advantage, likely because it times a wide range of physiological processes so that they occur at the most advantageous time of day. This project is focused on understanding the fundamental nature of the plant circadian clock and how it affects growth, reproduction, and crop yield. We are using the model plant Arabidopsis thaliana and the oilseed crop sunflower to better understand how the clock works and how it affects plant growth in the natural environment. Much of the work in the period of review has focused on how the clock, light, and environmental cues regulate late-stage floral development in sunflower and the implications for self- and cross-pollination. The ability to control the ability of sunflower to carry out these distinct types of reproduction is key to both breeders and growers. We have also made progress into our other research goals, albeit less than anticipated due to restrictions on research due to the ongoing pandemic. 1) Our first major objective is to characterize how environmental and internal cues affect floral organ growth to promote either outcrossing or selfing. We have discovered that the timing of pollen release by sunflower florets is extremely sensitive to changes in ambient temperature due to temperature-sensitive changes in the rate of style elongation. We found even small differences in floral temperature change the time of day pollen is first presented, the frequency of pollinator visits, and male reproductive success. A manuscript describing our findings will be submitted for publication within the next month. In related work, we have investigated the role of light and the circadian clock in late-stage floral development. We have found that these signaling pathways differentially regulate ovary, anther, and style development and work together to promote the synchronized development of dozens of florets on a sunflower head (capitulum) every day during the week-long period of floral anthesis. We have found that although early-stage floral development across a sunflower head is gradual and continuous, signals from the environment and the circadian clock work together to ensure that multiple rings of florets undergo late-stage developmental transitions at a single time of day. This discrete developmental program both promotes visits by pollinating insects and reduces the likelihood of self pollination. We are preparing these results for publication and plan to submit a manuscript within the next few months. 2) Our second major objective is to define molecular pathways controlling the timing of important plant traits in the field. One area of study is the regulation of growth pathways controlling sunflower solar tracking, or heliotropism. Our previous studies with chemicals that directly act on proteins that directly regulate cell expansion, plasma membrane proton pumps, showed that they could not activate the pumps during the night. These pumps are known to be controlled by phosphorylation. Therefore, we have carried out a quantitative phosphoproteomic time-course analysis of samples collected from the opposite sides of heliotropic stems. We have found statistically significant differences in proton pump phosphorylation at amino acids suggested to regulate pump activity on the east and west sides of stems at specific times of day. We are currently performing experiments in the model plant Arabidopsis thaliana to directly determine whether these phosphorylation events affect plant growth. We expect that these studies will reveal fundamental insights into how the circadian clock and the environment regulate plant growth processes in natural conditions. 3) Our last major objective is to better understand the molecular nature of the plant circadian clock itself and how it controls diverse plant growth pathways. During the period of review, we have made significant progress towards understanding the molecular function of XCT, a protein conserved across plants and animals. We previously found that the circadian clock runs fast in Arabidopsis thaliana plants mutant for XCT, a 'pioneer protein' without a known molecular function. During the period of review, we have found that XCT co-purifies with proteins important for splicing of messenger RNAs and that RNA splicing is altered in plants and yeast mutant for XCT. Moreover, our data suggest that XCT preferentially functions in the hours before dawn, suggesting a tantalizing link between the circadian clock and the fundamental cellular process of RNA processing. We are continuing work to better understand this connection, which may have important implications for cellular processes in both plants and animals.
Publications
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