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Molecular Characterization of a Novel Methionine-Rich δ-Kafirin Seed Storage Protein Gene in Sorghum (Sorghum bicolor L.)

¹School of Land and Food Sciences, The University of Queensland, St Lucia, QLD 4072, Australia. ²Present address: Centre for Plant Conservation Genetics, Southern Cross University, Lismore NSW 2480 Australia. ³Corresponding author. Phone: +61-7-3365-2141. Fax: +61-7-3365-1177. E-mail: i.godwin@uq.edu.au

We have isolated, cloned, and characterized a 660 bp full length cDNA encoding a putative seed storage protein gene, δ-kafirin (AY834250), from developing seeds of sorghum (Sorghum bicolor) inbred line SPV- 475. Translation of the DNA sequence predicts a 16-kDa polypeptide (precursor) of 147 amino acids, rich in methionine residues (17%). Reverse Transcriptase-PCR (RT-PCR) and Real Time-PCR revealed δ-kafirin is only expressed in developing seeds. δ-Kafirin exhibited 96% identity with another methionine-rich sorghum seed storage protein (AY043223). Interestingly, this δ-kafirin gene contained two insertions rich in ATG codons encoding five more methionine residues than AY043223. Comparison of the sorghum δ-kafirin proteins with other seed storage proteins from maize, rice, and Brazil nut revealed conserved domains, mainly at the N-terminus. This similarity, in particular to the zeins, suggests these proteins shared a common ancestor and that the variation observed occurred after the separation of the species.