Exploiting Brachypodium distachyon to elucidate on drought resistance mechanisms in grasses

: Linking transcript expression with phenotypical changes

Abstract

Understanding the molecular activities behind drought resistance traits are of increasing economic and environmental value as precipitation patterns fluctuate and the demand for sustainable food and fuel resources rises. Drought stress
triggers a whole plant response, involving a cascade of signaling and transcription networks which result in various physiological and metabolic changes. This BBSRC funded PhD project set out to investigate the mechanisms behind drought resistance in grasses. With the support of the industrial sponsors, DLF Trifolium, the aim was to develop the methods necessary to identify those molecular markers in above-ground plant tissue that relate to drought resistance and with an eye to evaluating if changes in cell wall characteristics may be attributable to this resistance. Aberystwyth University hosts a large Brachypodium distachyon germplasm collection, an undomesticated model grass exhibiting a wide range of natural variation. A two phase robust drought screening process was developed, from which candidate ecotypes for molecular analysis were selected from 137 Brachypodium ecotypes. These ecotypes displayed the greatest range in drought
response, making them excellent candidates for future phenotype and molecular analysis. This screen was then adapted and applied to a total of 68 forage and turf Lolium perenne lines for the selection of candidate plants in a drought resistant grass breeding programme at DLF Trifolium. RNA sequencing analysis of one drought susceptible and two resistant ecotypes was conducted and the resulting reads assembled to create a transcriptome reference for differential gene and transcript expression analysis between wellwatered controls and drought stressed plants. Additionally, cell wall biochemical analysis was carried out. The findings from these studies elucidate on specific drought resistance mechanisms. Transcriptome analysis identified unique highly expressed secondary metabolites associated transcripts in drought resistant ecotypes and the combination of physiological and transcriptome data indicate that differences in drought responses, despite similar co-expression, result from developmental variations between ecotypes. Finally, this study provides a foundation for the relatively unstudied relationship between cell wall composition
and drought tolerance.

Date of Award	2015
Original language	English
Awarding Institution	Aberystwyth University
Supervisor	Maurice Bosch (Supervisor) & Luis Mur (Supervisor)