Please use this identifier to cite or link to this item: http://hdl.handle.net/2440/92332
Type: Thesis
Title: Cell type-specific manipulation of salt tolerance genes in wheat and barley.
Author: Krishnan, Mahima
Issue Date: 2013
School/Discipline: School of Agriculture, Food and Wine
Abstract: More than 67% of Australian cropping land is at risk of becoming saline and agriculture is increasingly utilising salt effected land (Rengasamy, 2002). Salinity has a significant impact on crop yield, and the identification and manipulation of genes that help to ameliorate yield penalties resulting from salinity can enhance agricultural production. Bread wheat, a hexaploid with AABBDD genome, has been long considered more salt tolerant than the tetraploid durum wheat with an AABB genome. The D genome, originally from Aegilops tauschii, contains a locus important for maintaining high K⁺/Na⁺, Kna1, on chromosome 4, which contains the HKT1;5 gene encoding a Na⁺ specific transporter, TaHKT1;5-D. The transcript of this gene was knocked down through RNAi. Plants containing the RNAi construct were found to accumulate higher levels of Na⁺ in the 4th leaf regardless of whether they were grown under control or mild salt stress conditions (75mM). This result supports previous findings that orthologues of HKT1;5 in other plants influence Na+ translocation from root to shoot (Ren et al., 2005; Davenport et al., 2007). The impact of TaHKT1;5 on salt tolerance was studied by subjecting transgenic plants to control or salt stress (75mM) conditions. Changes in phenotype were measured through non-destructive plant imaging (LemnaTec® Scanalyzer), but no phenotypic variation was observed as a result of the salt stress that was applied, suggesting the stress may have been too mild. In parallel with the knockdown approach, the HvHKT1;5 gene, an orthologue of the bread wheat Na⁺ transporter (TaHKT1;5-D), and a barley inorganic proton pyrophosphatase, HvHVP1, were overexpressed in barley through use of promoters thought to control cell type-specific expression. Promoters were identified through an MPSS database search for genes with low to moderate transcript levels and specificity for root-cortex or root-stele. The promoters controlling these genes were then isolated to drive HvHKT1;5 in root cortex and stele and HvHVP1 in root cortex. Four promoters were found to be promising: two stelar-specific and two cortex-specific and were placed upstream of HvHKT1;5 and HvHVP1. These constructs were then transformed into barley (cv. Golden Promise). Transgenic plants were grown in 100mM salt stress with two independent lines for each promoter:gene construct. Independent lines which included a stelar-specific promoter controlling HvHKT1;5 transcription showed reduced Na⁺ accumulation and increased K⁺ accumulation in 4th leaf xylem sap. Transgene mRNA was detected in both shoots and roots of the plant. In conclusion, while lowering levels of HKT1;5 transcript in wheat were not found to impact whole plant salinity tolerance, it did increase Na⁺ accumulation in the shoot. This was supported by the results in barley where overexpression of HvHKT1;5 resulted in lower Na⁺ levels and a concomitant increase in K⁺ levels in the shoot. Further study on whether this result impacts barley salt tolerance is currently underway.
Advisor: Jacobs, Andrew Keith
Tester, Mark Alfred
Dissertation Note: Thesis (Ph.D.) -- University of Adelaide, School of Agriculture, Food and Wine, 2013
Keywords: salinity; cell type-specific expression; wheat; barley; HvHKT1;5; HvHVP1; TaHKT1;5-D
Provenance: This electronic version is made publicly available by the University of Adelaide in accordance with its open access policy for student theses. Copyright in this thesis remains with the author. This thesis may incorporate third party material which has been used by the author pursuant to Fair Dealing exceptions. If you are the owner of any included third party copyright material you wish to be removed from this electronic version, please complete the take down form located at: http://www.adelaide.edu.au/legals
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