Over the past half-century, the human population has doubled but food production has more than kept pace, and the fraction of people with insufficient food has declined.  Nonetheless, ~1 billion people remain chronically underfed and another ~2 billion suffer from micronutrient deficiencies. Global population growth and increased per capita consumption associated with greater wealth will require continued increases in agricultural production, necessitating an estimated doubling of crop production between 2005 and 2050. There is also a pressing need to make agriculture more sustainable; excess water use, unsustainable soil management, and fertilizer leaching all must be addressed. 

There are many challenges to increasing food production, but drought has been argued to pose the greatest threat to global food stability -- around 60% of the food produced worldwide relies entirely on rain for its water.  In the United States, agriculture is the major user of ground and surface water, responsible for ~ 80 % of national water consumption.Several climate models predict that continued increases in human-produced greenhouse gas emissions will dramatically increase the risk of droughts of unprecedented ferocity in regions including the US southwest and central plain. Throughout the continental US the number of consecutive days without rain is predicted to increase during the summer. Therefore, water-use efficiency is therefore likely to be an increasingly critical determinant of yield in crops and fitness in wild species. 

Our project has investigated the genetic underpinnings of plant water use in the crop species Brassica rapa.  The match between a plant’s endogenous circadian rhythm and external abiotic conditions, including water stress, can dramatically affect a plants ability to harvest light energy into photosynthetic products such as food, fuel, and fiber.  Brassica rapaexhibits a strong association between its daily circadian rhythms, water-use efficiency and its components, photosynthesis and transpiration. We have identified at least ten genetically defined regions that affect water-use efficiency. Of these, six co-localize with genes affecting circadian clock function, supporting a linkage between plant water use and the circadian clock.

Previous studies had shown that drought stress causes changes in the activities of genes at certain times of day. To investigate this further, we studied how young B. rapaplants grown in a controlled environment with a steady supply of water responded when watering stopped. Even before the plants show obvious signs of drought stress such as wilting, there are extensive changes in the expression of many genes.  We used an analysis technique to bring together all of the data into a network based on similar patterns of changes over time. This identified groups of genes whose changes in activity match the timing of the observed changes in the opening and closing of stomata, photosynthesis and other processes. These represent very early responses to drought stress in the plant. This work emphasizes the importance of time of day on plant stress responses. Changes that occurred only in the morning could not have been detected by measurements taken in the afternoon, and vice versa. The next step will be to find out which of the changes observed in this work are most important in making plants resistant to drought. These findings may help to develop strategies that would improve drought resistance in crop plants. We have also extended circadian-performance associations to include wild relatives of Brassicarapain field and growth-chamber studies.

Brassicaspecies are morphologically diverse. Both reproductive organs and vegetative features are highly modified among varieties of B. oleraceaand B. rapa. Distinct B. rapaaccessions have undergone selection for increased allocation to above-ground organs (i.e. leaves in cabbage, pak choi, and turnip green crops and seeds in oilseed types) as well as below-ground organs (i.e. in turnips). Our past studies provide evidence of genotypic variation in circadian clock period. Now we have shown that circadian differences generalize to crop morphotype, which may inform breeding for crop improvement. 

We conducted a controlled breeding program to develop new Advance Intercross Recombinant Inbred Line populations (AI-RILS), each of which was founded by founding crosses between morphologically diverse B. rapa accessions and the seed-oil crop R500 as common maternal parent. We are using these populations to further investigate the interplay between the circadian clock and drought responses.  In addition, we will make these materials available to the larger scientific community for their use in other types of experiments.

We are also continuing development and dissemination of K-16 educational resources based on genetic and genomic resources based on the rapid-cycling FPsc B. rapa model system. We are training middle and high school teachers to implement these educational modules via annual summer institutes at UW-Madison, through workshops offered at state and national teacher conventions, as well as ad hoc remote workshops made possible by travel to those national conventions. Thus, our ongoing outreach efforts are becoming manifest on state, national and international levels.

Last Modified: 05/31/2018
Modified by: C. Robertson Mcclung