Kernel-specific cDNA clones encoding three different isoforms of seed storage protein glutelin from oil palm Elaeis guineensis

The mRNA differential display method was used to identify and isolate cDNAs corresponding to transcripts that accumulate during the period of lipid synthesis, 12-20 weeks after anthesis (WAA) in the kernel of Elaeis guineensis, var. Tenera. We successfully isolated two cDNA clones, KT7 (312 bp) and KT8 (266 bp). Interestingly, both clones show 79% nucleotide sequence identity to each other. This suggests that both clones encode the isoforms of the same protein. We screened the kernel (15 WAA) cDNA library and isolated the clone pKT7 (587 bp) using KT7 as probe, and isolated another isoform with KT8 probe, which designated as pKT9 (900 bp). Clone pKT9 has 93% nucleotide identity to KT8 and only 46% to pKT7 in their 3'-untranslated region. All three clones displayed significant amino acid sequence identity to seed storage protein glutelin from monocotyledon and globulin from dicotyledon plants. The coding sequence of KT8 (106 bp) shows 76 and 97% identity to pKT9 and pKT7, respectively. Therefore, we suggest that clones KT8 and pKT7 are members of the same subfamily (A), while pKT9 belongs to another subfamily (B) of glutelin multigene families. Southern analysis shows that there are at least four members for the subfamily B. Northern analysis shows that these three members of the glutelin family are co-ordinately expressed and developmentally regulated during the development of the kernel. The transcripts begin to accumulate at 12 WAA, increase in 15 WAA and show a significant reduction at 17 WAA.