Stomatal characteristics and water use efficiency in Arabidopsis thaliana flowering time transcription factor mutants

Heather Pence, Purdue University

Abstract

Water is the most limiting factor for crop production. These issues necessitate the study of water use efficiency (WUE; CO2 assimilated/H2O transpired), an important trait of plants, particularly crop species. The need to develop crops with higher WUE is becoming increasingly urgent as global water shortages continue and periods of agricultural drought increase. Consequently, the genetic basis of WUE is of great interest for manipulation in plant breeding improvement programs to reduce water consumption, maintain yield stability, and food security as the world population continues to grow. Much attention has been paid to determinants that affect water use, such as ABA metabolism and the regulation of stomatal dynamics and density. However, WUE is also largely dependent on the timing of life cycle completion in the plant; longevity requires a higher efficiency if plants are to survive in environments with low water availability. Specifically, a linkage has been consistently observed in nature between flowering time and overall WUE. Recent quantitative trait loci (QTL) data in Arabidopsis thaliana indicate that flowering time and WUE QTL co-locate with one another; FLOWERING LOCUS C (FLC) was identified as a candidate flowering time transcription factor that acts on other unknown determinants that also affect WUE, as measured by carbon isotope discrimination (CID). FLC is a central floral repressor that, when up-regulated, suppresses the transition to flowering in A. thaliana. These QTL data provide direct evidence for linkage of these traits on a molecular level. It is unknown whether the genetic linkage of these traits is due to pleiotropic effects or coordinated selection on specific groups of alleles that affect both traits, as flowering time and WUE are both heritable traits. Thus, the extent to which these traits can be regulated and/or separated is critical for future breeding programs designed to selectively improve WUE. Therefore, the central hypothesis for this research is that flowering time transcription factors also regulate WUE in A. thaliana. Experiments were specifically designed to test several measures of WUE and traits associated with WUE e.g. stomatal density, transpiration, water loss, etc., in a collection of A. thaliana flowering time transcription factors mutants. CID data from three genotypes is consistent with previously published values and suggests that the delayed flowering genotype ColFRI has increased integrative WUE. However, no differences in instantaneous and integrative measures of WUE were detected in any genotype, which indicates that this group of flowering time transcription factors does not regulate WUE in A. thaliana. Transpiration rates, with the exception of one genotype, and diurnal water loss also did not differ among these genotypes. This is consistent with the WUE data. Transpiration and diurnal water loss did show the expected negative correlation with integrative WUE despite the lack of significant differences among genotypes for these three traits. This group of genotypes did display interesting stomatal patterning phenotypes. Specifically, almost all delayed flowering genotypes had reduced abaxial stomatal density. But, this reduction in abaxial stomatal density was compensated for by a subsequent increase in adaxial stomatal density in these genotypes. This compensation in stomatal density resulted in very few genotypes that differed from the wild type in total stomatal density (abaxial plus adaxial stomatal density). Therefore, all late flowering genotypes displayed significantly lower abaxial:adaxial stomatal ratios that the wild type genotypes. Lastly, results from this research suggest that it is not sufficient to examine only the abaxial epidermis for stomatal characteristics, as both abaxial and adaxial stomatal density are significantly correlated with total stomatal density, but do not have a significant correlation with each other. All genotypes responded similarly with stomatal patterning phenotypes in long day (LD) and short day (SD) conditions as well, which suggests that the phenotype is photoperiod independent, even though this hypothesis was not explicitly tested. However, not all delayed flowering genotypes display the same response in stomatal density overall. Therefore, this alteration in stomatal patterning is not simply a result of altered rosette leaf development, but rather endogenous signals that are affecting patterning of the abaxial and adaxial epidermises.

Degree

M.S.

Advisors

Mickelbart, Purdue University.

Subject Area

Plant sciences

COinS