Aluminium-induced gene expression in sugarcane roots.

Abstract

Due to the increasing prevalence and severity of Al phytoxicity in certain regions of the South

African sugar industry, a research programme has been initiated at SASEX to elucidate the

molecular mechanisms by which sugarcane detects and responds to the metal. As part of this

larger investigation, the current study aimed to assess the response of a reportedly Al tolerant

cultivar, Saccharum spp. hybrid cv. N12, to phytotoxic levels of Al. Hydroponically-grown

plants of this commercial genotype were used in Al inhibition studies, the results of which

indicated that exposure of plants to 250µM Al for 24 hours resulted in maximum reduction of

root elongation. Under these conditions, root growth was inhibited by approximately 36%,

compared with only 4% for the 50µM Al treatment. Subsequently, this exposure regime was

used to gather the terminal 5 to 10mm of root tips, the site of the primary Al lesion, of

challenged and control, unchallenged plants for molecular analysis.

Total RNA was extracted from the Al challenged and control root tips, from which mRNA was

subsequently isolated, reverse transcribed and converted to double-stranded cDNA. The two

populations of cDNA were reciprocally subtracted from each other and used to construct

subtractive cDNA libraries in Lambda ZAP®II phages. Randomly selected clones, 576

representatives from each of the libraries, were screened using membrane-based array

technology. Results indicated that only 33% (190) of the Al-treatment specific library cDNAs

were found to be more highly expressed under conditions of Al stress than under control

conditions. Of these potentially Al response-related cDNAs, 25 were sequenced and submitted

to sequence databases for the assignment of putative identities. No genic sequences known to be

directly associated with the Al stress response were identified, however, several were found to

be related to pathogenesis or general stress pathways. Although further Northern hybridisation

work is required to validate these results, they suggest that the induction of general stress

response pathways may be involved in the aluminium stress response of this sugarcane cultivar.

Such Al stress-related sequences could have applications in marker-assisted breeding

programmes and as candidate genes for the genetic engineering of tolerant genotypes.