Expression of a Β-Expansin GENE in Wild Arachis in Response to Gradual Water Deficit

Peanut (Arachis hypogaea) is widely cultivated in the tropics, where unpredicted drought stress is a limiting factor for production. Conversely, wild species are found in extremely diverse environments; constituting a rich source of allele diversity for improving drought tolerance in peanut. Analysis of 380,601 Roche/454 reads from cDNA libraries of A. duranensis (wild diploid) plants submitted to gradual water deficit revealed differential expression of genes related to drought responses. The second most differentially expressed gene in silico was a β-expansin. Expansin belongs to a multigenic family involved in cell wall extension and, also implicated in drought stress tolerance. This work aims to characterize this gene and its expression pattern in roots during drought stress. The A. duranensis β-expansin cDNA (848pb) and its predicted genomic sequence (1320 pb) showed high degree of similarity (nucleotide and amino acid sequence) to previously described plants β expansins, including in A. hypogaea. The relative expression pattern of A. duranensis β-expansin evaluated by qRT-PCR in three wild Arachis species (A. duranensis, A. magna and A. ipaënsis) indicated its up regulation whenever water in soil was limited and basal expression whenever soil was rehydrated. Similarly, preliminary in situ hybridization data showed stronger hybridization signals in the cytoplasm of epidermis and xylem cells of the roots under drought stress than in re-watered roots of A. duranensis, A. magna and A. ipaënsis. Results suggest that β-expansin is conserved in Arachis and plays a role in drought response in wild Arachis species.

Financial support: Embrapa, CNPq and Generation Challenge Program.