Population-wide variation in response to salinity in Arabidopsis thaliana

Jessica N Brazelton, Purdue University

Abstract

Producing adequate food supplies in spite of an ever-increasing world population will continue to be increasingly difficult in part due to environmental constraints. As much of the world's agriculture is produced utilizing irrigated land, salinity stress is a growing problem. The focus of this research was to better understand natural variation in salinity tolerance, ion accumulation differences under salinity stress, and polymorphisms of the Na+ transporter, AtHKT1;1 that may lead to plastic or constitutive changes in AtHKT1;1 function that may be of adaptive significance. Natural variation in leaf K+ and Na+ accumulation in plants grown in the absence and presence of NaCl stress was measured using inductively coupled plasma mass spectrometry in 314 accessions and a Tsu-1 x Kas-1 RIL population of Arabidopsis thaliana. Candidate loci contributing to ion accumulation were determined by quantitative trait loci mapping and genome-wide association mapping. AtHKT1;1 was determined to be the major loci contributing to variation in leaf Na + accumulation under all conditions, while K+ accumulation was under polygenic control with genetic associations that changed under salinity stress. Candidate loci for natural variation in salinity tolerance were also determined for the 314 accessions and Tsu-1 x Kas-1 RIL population using QTL mapping and genome-wide association mapping. Plants were grown in a common garden experiment and treated with 100 mM NaCl until all plants were recorded dead. It was determined that salinity tolerance is under polygenic control and may have some interactions with the flowering time pathway, as many of the tolerant accessions exhibited a delay or inhibition of bolting when under salinity stress, and a tolerance QTL was identified linked to FRI in long days, which was lost when plants were grown on short days. While the causal polymorphism(s) driving natural variation in AtHKT1;1 function could not be determined from the AtHKT1;1 DNA sequence, sequence analysis did reveal a high rate of DNA sequence polymorphism at this locus, though the Tajima's D calculations did not deviate from the background levels for A. thaliana. Furthermore, gene expression studies for AtHKT1;1 revealed variation in the capacity of accessions to induce AtHKT1;1 expression after NaCl treatment, suggesting that significant natural variation exists in the plasticity of AtHKT1;1 function in response to NaCl stress, though further determination of population-wide selective sweeps or signatures of molecular evolution are necessary to further validate if this variation in adaptive. Furthermore, field experiments will be necessary to fully test this hypothesis.

Degree

Ph.D.

Advisors

Salt, Purdue University.

Subject Area

Genetics

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