Stem specific promoters from sorghum and maize for use in sugarcane
Date
2008-12
Authors
Govender, Cindy
Journal Title
Journal ISSN
Volume Title
Publisher
Stellenbosch : Stellenbosch University
Abstract
Sugarcane (Saccharum spp.) is an important crop which is cultivated worldwide for the
high sucrose content in its stem. Conventional plant breeding has proven to be very
successful over the years with regard to the enhancement of yield characteristics but due
to the exhaustion of genetic potential in the commercial sugarcane germplasm recent
progress has been slow. Genetic engineering seems to be a more attractive approach to
enhance sucrose content and pest resistance in the stems but requires appropriate
transgenes and suitable promoter.
A promoter is essential to drive the transcription of a gene and is therefore critical to the success of transgenic approaches in sugarcane crop improvement. A negligible number of
strong stem-specific promoters is available for use in sugarcane and this is one of the major limitations to genetic engineering. The goal of this project was to isolate a stemspecific promoter from maize and sorghum to drive stem-specific transgene expression in sugarcane.
The approach used was to source promoters from non-sugarcane grass species with less
complex genomes to simplify isolation and possibly counteract silencing. A cDNA
sequence (SS) (EST clone, Accession number AW746904) from sugarcane was shown by
Northern and Southern analysis to be stem-specific and to have an appropriately low
copy number. The SS gene sequence was not expressed in the leaves of maize, sorghum
or the sugarcane cultivars and prominent expression was observed only in the stems of
the sugarcane hybrids N19 and 88H0019.
The SS gene sequence was used to isolate its upstream regions from a Lambda genomic
library of maize (Zea mays) and a sorghum (Sorghum bicolor) Bacterial Artificial
Chromosome library (BAC). Of the four sorghum and six maize clones obtained in this study, a 4500 bp maize genomic DNA fragment (λ5) was sub-cloned in three fragments
into separate pBluescript vectors using the ‘forced’ cloning approach for sequence and
database (BLASTN) analysis. This revealed the complete SS gene sequence (975 bp),
the promoter and a 300 bp intron region.
A stretch of DNA sequence from nucleotides 664-3194 from the maize clone 5 sequence
was designated the maize5-pro. Following sequence alignment of the maize and
sugarcane promoter regions, significant sequence identity (68%) was observed between
nucleotide 1675 and 3194 in maize and nucleotide 1506 and 2947 in sugarcane. The
distance between the putative TATA-box and the TSS for this promoter (30 bp) was
found to fall within the expected range of 32± 7 bp.
The promoter region was analysed for possible cis-acting regulatory elements and
revealed several promoter elements that are common in other plant promoters. The
comparisons made between the putative transcription factors in maizepro-5 and the
sugarcane promoter show that both promoter sequences are very similar as they share ten of
the same transcription factors. However, the transcriptional factors WBOX, SRE and
SP8BFIBSP8BIB are unique to the maize5-pro and the TAAG motif to the sugarcane
promoter.
Primers were designed with appropriate restriction sites and the promoter and intron
(2850 bp) region was amplified by PCR (Polymerase chain reaction). The amplified
fragment was fused inframe to the GUS reporter gene encoding β-glucuronidase to
produce a transformation test vector. This will be used in future work to assess the
functionality of the promoter through the production of stable transformants in which
GUS activity can be measured in a range of tissues.
Description
Thesis (MSc (Genetics. Institute of Plant Biotechnology))--Stellenbosch University, 2008.
Keywords
Sugarcane, Promoters, Sorghum, Maize, Dissertations -- Genetics, Theses -- Genetics