Physiological Basis of Abiotic Stress in Helianthus

Although wild plants have evolved mechanisms for dealing with stress, crop plants may have experienced trade-offs during domestication as breeders selected for traits related to high growth and productivity. In Helianthus specifically, the productivity of cultivated sunflower (Helianthus annuus) is often very limited by environmental conditions whereas wild Helianthus is found in a wide-range of ecosystems (e.g. desert, saline, and coastal dunes). As a lab, we seek to understand the physiological basis of several abiotic stresses in both cultivated H. annuus and stress-adapted, wild Helianthus species that are potential donors of beneficial alleles.  These abiotic stresses included drought, salt, and low nutrient stress.


Drought Stress

Evolution of stem and leaf traits related to water transport and use in wild Helianthus

Wild sunflower species grow in a variety of habitats, ranging from desert sand dunes and granite outcrops to grassy fields and wetlands. Alex Pilote seeks to understand how closely related Helianthus species adapted to exist in such a breadth of water availability. He also studies the overall coordination between stem and leaf traits, which his research has thus far shown to have evolved in a correlated fashion.


Photo Description: Leaf, stem cross-section, and vascular tissue of two wild Helianthus species (a. H. agrestis and b. H. argophyllus). Scale bars are 2cm, 2mm, and 0.2mm from left to right.


Does cultivated Sunflower respond differently to depending on the ontogenetic stage?

Water limitation is the most limiting abiotic stress on crop yield. One complexity in testing any sort of drought response is that the cumulative impact of drought on plant performance is dependent on the developmental stage of the plant during drought. Furthermore, it is possible that a particular drought resistance "strategy" could be more successful at one developmental stage than at another. Therefore, Ashley Rea aims to identify physiological traits that correlate with resistance to water limitation and determine if this changes with ontogenetic stage. 


Do cultivated and wild Sunflower respond differently to drought?

During domestication, traits related to abiotic stress resistance may have been lost as breeders selected for maximum growth and productivity. To explore potential trade-offs, Torey Burns seeks to determine how cultivated and wild Helianthus annuus differ in their responses to water limitation.

A sunflower plant wilts after water is withheld

Photo description: A sunflower plant wilts after having water withheld.


Extensive drought screening of cultivated Sunflower in the field

With global population levels rising and changing environments due to climate change, producing enough food to feed everybody is a growing challenge. One of the ways to meet this challenge is to breed sturdier crops that can tolerate environmental stress better than current high yielding crop varieties allowing for better use of poor agricultural land. Post doc Andries Temme aims to better our understanding of both how plant traits confer stress tolerance in cultivated Sunflower and how these traits are regulated in the genome.

Currently, Andries is carrying out an extensive drought tolerance screening of 289 cultivated sunflower genotypes in the Imperial Valley, CA.  We harvest the plants at maturation and monitor their performance and various traits via traditional (high effort) and high throughput sensor based measurements in the meantime. These experiments will give us candidate genotypes as well as inform us which plants are associated with high stress tolerance. Additional studies on select genotypes will then delve into determining the genes and mechanisms behind those traits.


Salt Stress

Extensive salt screening of cultivated Sunflower in the greenhouse

Similar to project described above, Andries Temme aims to carry out an extensive salt tolerance screening of 289 genotypes of cultivated sunflower in the greenhouse. He aims to identify candidate genotypes with high tolerance of salt as well as determine plant traits correlated with high salt stress. Downstream studies will identify genes and mechanisms related to salt stress.


Nutrient Stress

How do nutrient acquisition efficiency and nutrient use efficiency affect the overall performance of cultivated Sunflower?

An understanding of nutrient use needs to consider nutrient acquisition efficiency (NAE) and nutrient use efficiency (NUE). These categories represent trait correlation networks employed by plants to both acquire and utilize nutrients. 

While a genotoype’s nutrient efficiency is typically measured strictly by yield performance, the whole-plant measure of nutrient efficiency is also important to understanding plant nutrient use. As such, it is likely that genotypes differ in their nutrient allocation patterns between above and below ground organ mass in addition to differing in NAE and NUE. Therefore, Ashley Rea aims to identify the extent to which NAE and NUE effect overall plant performance at varying fertilization levels while accounting for organ type.


Evolution of nutrient resorption in wild Helianthus

Nutrient utilization efficiency (NUE) is determined by nutrient productivity and mean residence time (MRT). MRT is determined by leaf lifespan (LL) and nutrient resorption (NR). NR is the process by which nutrients housed in senescing leaf tissues are conserved via remobilization to other plant organs/tissues.

Meanwhile, the other component of MRT (leaf lifespan), is considered a key trait in the leaf economics spectrum (LES). Within the LES, species sort along an axis ranging from fast-growing, resource-acquisitive species bearing short-lived leaves with high photosynthetic rates and high nutrient content to slow-growing, resource-conservative species with long-lived, sturdy leaves that have lower photosynthetic rates and nutrient contents. It is possible that NR is also an important trait in the LES; because NR necessarily involves the recycling of nutrients rather than the acquisition of them, it would be expected that high rates of NR correlate with the “conservative” end of this spectrum. Furthermore, if high NR is a resource-conservative trait, we would expect to see evidence of adaptive differentiation wherein high NR is present in low-fertility habitats. Therefore, Ashley Rea aims to determine if NR is adaptive and if evidence exists for correlated trait evolution of NR with other resource conservative traits.


Extensive low nutrient screening of cultivated Sunflower in the greenhouse

Andries Temme screened 289 cultivated sunflower genotypes in the greenhouse for resistance to low nutrient stress. This study will provide him with candidate genomes with high tolerance of low nutrient stress as well as provide him with additional understanding of plant response to low nutrient stress. Downstream studies will give us a greater understanding of the traits correlated with resistance to low nutrient stress as well as identify correlated genes.