Molecular characterisation of a novel methionine-rich delta-kafarin seed storage protein gene in sorghum (Sorghum bicolor L.)

We have isolated, cloned, and characterized a 660 bp full length cDNA encoding a putative seed storage protein gene, delta-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 delta-kafirin is only expressed in developing seeds. delta-Kafirin exhibited 96% identity with another methionine-rich sorghum seed storage protein (AY043223). Interestingly, this delta-kafirin gene contained two insertions rich in ATG codons encoding five more methionine residues than AY043223. Comparison of the sorghum delta-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.