Indian mustard (Brassica juncea) grown on land with elevated arsenic concentration can absorb and accumulate high levels of arsenic. B. juncea is an important oil-bearing crop and broadly grown in Bangladesh and West Bengal, where the land is heavily contaminated with arsenic. Arsenic is documented as a group 1 carcinogen and can enter the biosphere through the food chain. With the high population density and a heavy agriculture-based economy in Bangladesh and West Bengal, issues related to food safety must be addressed to solve the problems associated with arsenic accumulation in B. juncea seed oil, which is caused by B. juncea tolerance to arsenic toxicity. Therefore, it is important to study the variation of arsenic tolerance among different Indian mustard cultivars and to understand the genetic mechanisms of arsenic tolerance in Indian mustard. Such results from the study could help to reduce potential arsenic toxicity in both plants and humans through diet as well as to benefit local agriculture industry in Bangladesh and West Bengal. In this research, a consistent trend was found between arsenic concentration and biomass accumulation in all B. juncea cultivars. When arsenic concentration increases, the biomass accumulation decreases. A positive correlation was identified between arsenic tolerance levels in B. juncea roots and arsenic absorption in the seed and seed oil. The observation of these correlations in B. juncea suggests that breeding arsenic resistant B. juncea cultivars could increase plant yield but may inadvertently lead to an increased arsenic concentrations in the seed and seed oil. However, variations in arsenic accumulation were observed in both arsenic resistant and susceptible cultivars, which provide possibilities to breed high arsenic-tolerant and low arsenic-absorptive strains of B. juncea. To study the genetic mechanisms underlying arsenic tolerance variation in Indian mustard, the model plant Arabidopsis thaliana was employed. Arsenic tolerance of various A. thaliana accessions was measured and arsenic tolerance genes were screened using a genetic mapping approach. Since no consistent trend was found between arsenic concentrations and arsenic tolerance in A. thaliana root and shoot tissues, it suggests that arsenic has a complex impact on those phenotypes examined in A. thaliana. To study the mechanisms underlying genetic variation of A. thaliana for arsenic tolerance, gene mapping including quantitative trait locus (QTL) mapping and genome-wide association mapping (GWAS) was employed to identify targeted genomic regions and candidate genes. One recombined inbred population was employed in QTL mapping and a worldwide collection of 39 A. thaliana accessions was used in GWAS analysis. QTL mapping analysis and GWAS revealed similar genomic regions and candidate genes. Among all revealed candidate genes, one gene (gene ID: At5G05560) with a known function of abiotic stress resistance was identified, which may be related to plant arsenic tolerance or detoxification. To understand the function of this gene, however, requires further analysis. Other genes associated with arsenic tolerance or detoxification function in the genetic region selected from gene mapping study may also be identified by further analysis. The functional analysis of candidate genes, and the molecular markers selection from revealed genomic regions could be applied to contribute to breeding B. juncea strains with higher arsenic tolerance and lower arsenic accumulation.
|Date of Award||1 Mar 2017|
|Supervisor||Roderick Scott (Supervisor)|