Isolation and expression analysis of transcripts encoding metallothioneins in oil palm

Abstract

Two of the abundant transcripts encoding type 2 metallothionein (MT) proteins designated as MET2a and MET2b were selected in our previous study due to their high abundance (16.05 %) in the suppression subtractive hybridization library and their involvement in fruit development and maturation. The present study involves the isolation of the full-length cDNA encoding MET2a and MET2b from the ripening oil palm fruit mesocarp, examining their expression pattern compared to the other two previously reported type-3 MT members (MT3-A and MT3-B) in various oil palm organs including different vegetative and reproductive tissues. The full-length cDNA sequences of MET2a and MET2b were 571 and 553 bp and they were designated as EgMT2a and EgMT2b, respectively. The sequences of the EgMT2a and EgMT2b were then compared for sequence similarities in the database using both BLASTN and BLASTX programs. Their sequences were homologous (67 -77 %) with several type-2 MTs in plants. All four MT encoding genes were differentially expressed in the ripening oil palm mesocarp tissues, but undetectable in the vegetative tissues examined. All MT genes examined were significantly up-regulated in the mature developmental stages of oil palm fruit mesocarp, except for EgMT2b which was expressed only at 17 weeks after anthesis. The type 2 MT proteins are related to a greater degree to the late fruit-ripening stage than the type 3 MT proteins consistent with their reported functions in homeostasis or detoxification. The findings in the present study contribute to better understanding the molecular mechanisms involved in fruit ripening in oil palm.

Expression analysis of metallothioneins and mineral contents in tomato (Lycopersicon esculentum) under heavy metal stress

“…MT3 gene expression is slightly suppressed when exposed to Fe and Cu, while it increased slightly with the treatment of Mn and Zn in tomato . The highest expression of MT3 increased in ripened fruits of Elaeis guineensis . Also, MT3 gene was expressed in roots, leaves, flowers, cotyledon and hypocotyls of Brassica napus .…”

“…24 The highest expression of MT3 increased in ripened fruits of Elaeis guineensis. 18 Also, MT3 gene was expressed in roots, leaves, flowers, cotyledon and hypocotyls of Brassica napus. 44 We found in this study that MT4 transcript expression significantly increased in fruits of tomato exposed to both Cu and Pb, and other tissues did not show a clear change.…”

“…These MTs are induced by various heavy metals and expressed at different levels in plant tissues. The expression characteristics of MTs differ according to species and tissues . MT1 is predominantly expressed in roots and leaves, MT2 is expressed primarily in leaves and stems, MT3 is expressed in ripening fruits, and MT4 is usually expressed in developing seeds …”

“…Although some studies of various plants such as Lycopersicon esculentum , Populus trichocarpa x deltoides , Arachis hypogaea Populus alba , Gossypium hirsutum , Glycine max , Kandelia candel , Elaeis guineensis and Ziziphus jujupa have worked on gene expression, there is no general conclusion about the expression of MTs. Most research focused only on one MT type or plant tissue.…”

“…The expression characteristics of MTs differ according to species and tissues. 18 MT1 is predominantly expressed in roots and leaves, MT2 is expressed primarily in leaves and stems, MT3 is expressed in ripening fruits, and MT4 is usually expressed in developing seeds. 19,20 Plants take up heavy metals and accumulate them in different organs.…”