Genetic Analysis Of Ximenia Americana Under Natural Conditions

Abstract

Cross-species hybridization approaches have been used for genetic analysis of species

that do not have complete genome arrays available. The study used the cross-species

DNA-DNA hybridization approach to characterize Ximenia americana biological

processes. Preliminary micro-array studies done in the Department of Chemistry and

Biochemistry at the University of Namibia has created X. americana DNA-DNA

hybridization to a well-known Arabidopsis thaliana genechip (ATH1). A. thaliana

probe-pairs that hybridised to the X. americana genomic DNA on the basis of the

perfect-match (PM) probe signal were selected and analysed using a cel file parser script

to generate a new high density probe mask files. These files effectively represent the

first ever X. americana DNA-DNA hybridisation data. This study conducted gene

ontology analysis of X. americana/A. thaliana hybridisation data. Such gene ontology

analysis demonstrated that abiotic stress response genes are over-represented in relative

comparison to model species A. thaliana under natural conditions. This observation was

independently confirmed with PCR amplification of the following orthologous genes

using X. americana genomic DNA: AT4G15910.1, SAD2, HXK1, ACC and ERF/AP2.

Given the lack of genomic sequence information in X. americana background, primers

for genomic amplification was design using A. thaliana genomic sequence information.

Primers where designed to yield 100 bp genomic PCR product. Each of the selected

genes was successfully amplified hence giving evidence of homology within primer

binding sites. Nonetheless, the genomic amplification of these key abiotic factors in X.

americana confirms the type of responses that supports the adaptation of X. americana

under natural conditions that are stress related (heat and drought stress). Although

transcript levels of this important abiotic response factors could not be measured in

absolute or relative terms, the study demonstrated inherent presence of such genes at the

genomic level of X. americana. Further studies will be required to demonstrate that

some sort of modification of any of these or other abiotic response factors within the

genome of X. americana provides the key basis for its adaptation to the relatively dry

and hot climatic conditions.