Differences in LEA-like 11-24 gene expression in desiccation tolerant and sensitive species of Linderniaceae are due to variations in gene promoter sequences.

Many desiccation induced late embryogenesis abundant (LEA) protein encoding genes have been identified from Craterostigma plantagineum Hochst. In the desiccation tolerant plants C. plantagineum (Cp) and Lindernia brevidens Skan (Lb) transcripts encoding LEA-like 11-24 protein are abundantly expressed during desiccation whereas in Lindernia subracemosa De Wild. (Ls), a desiccation sensitive plant, the LEA-like 11-24 transcripts are expressed at a low level. Since promoters determine gene expression, a comparative promoter analysis was carried out to decipher the underlying mechanisms of differential gene expression. Two transient transformation methods (particle bombardment and optimised Agrobacterium co-cultivation) were used to analyse the promoter activities of the Cp, Lb and Ls LEA-like 11-24 gene in homologous and heterologous systems. Minimal promoters were isolated from all three species and their promoter activities were assessed in response to mannitol or ABA. Particle bombardment or Agrobacterium co-cultivation yielded similar results. Site-directed mutagenesis was used to identify which cis-acting elements in the LEA-like 11-24 promoter fragments are crucial during mannitol and ABA treatments. The presence of these promoter cis-elements explains the differences in transcript abundance in the desiccation tolerant and desiccation sensitive species. Results indicated the importance of the drought responsive elements (DRE) element for promoter activity.