Abstract
In Latin America and sub-Saharan Africa, tropical maize (Zea mays L.) is a major crop for human consumption. To cope with the increasing population and changing environment, there is a need for improving tropical maize germplasm. As part of a biotechnological approach, efficient in vitro regeneration of two tropical maize inbred lines (CML216 and CML244) was established. A number of parameters were optimized, such as age of the immature embryos, plant media and growth regulator concentration. After 6 weeks of culture, somatic embryos that had already reached the coleoptilar stage produced shoots after light induction and developed into fertile plants after acclimation in the soil. The callus induction frequencies and somatic embryo-derived plantlet formation were higher when cultured with the Linsmaier and Skoog medium than those with the Chu’s N6 basal medium. Regeneration of tropical maize shoots depended on the 2,4-dichlorophenoxyacetic acid (2,4-D) concentration at the callus initiation stage from immature embryos. The recalcitrance of the tropical maize inbred line TL26 to in vitro regeneration was overcome in a single-cross hybrid with the CML216 and CML244 genotypes. Remarkably, tropical maize somatic embryos were formed at the abaxial side of the scutellum facing the medium, probably from the axis of the immature embryos, as shown by histological sections. Upon co-cultivation, agrobacteria transiently expressed their intronless β-glucuronidase-encoding gene at the embryogenic tissue, but not with an intron-containing gene, suggesting that virulence genes are induced in Agrobacterium, but that subsequent steps in the T-DNA transfer are inhibited.
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Abbreviations
- 2,4-D:
-
2,4-Dichlorophenoxyacetic acid
- bar :
-
Phosphinothricin acetyltransferase-encoding gene
- CIM:
-
Callus induction medium or resting medium
- CMM:
-
Callus maturation medium
- ESM/Inf:
-
Embryo suspension medium/infection medium
- GUS:
-
β-glucuronidase
- LS:
-
Linsmaier and Skoog
- MES:
-
2-(N-morpholino)ethanesulphonic acid
- MS:
-
Murashige and Skoog
- N6:
-
Chu’s N6 basal medium
- P35:
-
Cauliflower mosaic virus 35S promoter
- PIPES:
-
Piperazine-N,N-bis(2-ethanesulphonic acid)
- R0:
-
Regenerated shoot from somatic embryo
- R1:
-
Progeny of R0 shoot
- SIM:
-
Shoot induction medium or regeneration medium
- T-DNA:
-
Transfer DNA
- T35S:
-
Cauliflower mosaic virus 35S terminator
- Tnos:
-
Nopaline synthase terminator
- UBIL:
-
Maize long ubiquitin promoter
- uidA :
-
β-d-glucuronidase gene from Escherichia coli
- X-Gluc:
-
5-Bromo-4-chloro-3-indolyl-β-d-glucuronic acid
- YEP:
-
Yeast Extract Peptone
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Acknowledgments
We thank Dr. Martine De Cock for help in preparing the manuscript. S.E.A., A.J.M., and C.T. are indebted to the Vlaamse Interuniversitaire Raad, The Rockefeller Foundation, and the United States Agency for International Development for predoctoral fellowships, respectively.
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Anami, S.E., Mgutu, A.J., Taracha, C. et al. Somatic embryogenesis and plant regeneration of tropical maize genotypes. Plant Cell Tiss Organ Cult 102, 285–295 (2010). https://doi.org/10.1007/s11240-010-9731-7
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DOI: https://doi.org/10.1007/s11240-010-9731-7