Planta

, Volume 236, Issue 5, pp 1585–1598

Isolation and functional characterisation of banana phytoenesynthase genes as potential cisgenes

  • Bulukani Mlalazi
  • Ralf Welsch
  • Priver Namanya
  • Harjeet Khanna
  • R. Jason Geijskes
  • Mark D. Harrison
  • Rob Harding
  • James L. Dale
  • Marion Bateson
Original Article

Abstract

Carotenoids occur in all photosynthetic organisms where they protect photosystems from auto-oxidation, participate in photosynthetic energy transfer and are secondary metabolites. Of the more than 600 known plant carotenoids, few can be converted into vitamin A by humans and so these pro-vitamin A carotenoids (pVAC) are important in human nutrition. Phytoene synthase (PSY) is a key enzyme in the biosynthetic pathway of pVACs and plays a central role in regulating pVAC accumulation in the edible portion of crop plants. Banana is a major commercial crop and serves as a staple crop for more than 30 million people. There is natural variation in fruit pVAC content across different banana cultivars, but this is not well understood. Therefore, we isolated PSY genes from banana cultivars with relatively high (cv. Asupina) and low (cv. Cavendish) pVAC content. We provide evidence that PSY in banana is encoded by two paralogs (PSY1 and PSY2), each with a similar gene structure to homologous genes in other monocots. Further, we demonstrate that PSY2 is more highly expressed in fruit pulp compared to leaf. Functional analysis of PSY1 and PSY2 in rice callus and E. coli demonstrates that both genes encode functional enzymes, and that Asupina PSYs have approximately twice the enzymatic activity of the corresponding Cavendish PSYs. These results suggest that differences in PSY enzyme activity contribute significantly to the differences in Asupina and Cavendish fruit pVAC content. Importantly, Asupina PSY genes could potentially be used to generate new cisgenic or intragenic banana cultivars with enhanced pVAC content.

Keywords

Biofortification Carotene Cisgenic Intragenic Isoprenoid Metabolic engineering 

Abbreviations

PSY

Phytoene synthase

pVAC

Pro-vitamin A carotenoid

VAD

Vitamin A deficiency

Supplementary material

425_2012_1717_MOESM1_ESM.doc (122 kb)
Supplementary material 1 (DOC 122 kb)
425_2012_1717_MOESM2_ESM.jpg (1.5 mb)
Supplemental Fig. 2. Alignment of banana PSY partial protein sequences. Neighbour joining multiple sequence alignment of banana PSY1 and PSY2 partial protein sequences translated from the partial nucleotide sequences used in Fig. 1 (Table S3) and Cavendish PSY2b (Ma-PSY2b; GenBank Accession No. JX195666) (JPEG 1515 kb)
425_2012_1717_MOESM3_ESM.jpg (768 kb)
Supplemental Fig. 3. Comparative structure of PSY mRNA and genomic DNA sequences from Asupina and Cavendish cultivars. (a) Structure of putative Asupina (A) and Cavendish (Ma) PSY mRNA transcripts showing the coding region (black rectangle) between the start (AUG) and stop (UGA or UAA) codons of A-PSY1 (GenBank Accession No. JX195658), A-PSY2a (GenBank Accession No. JX195659), Ma-PSY1 (GenBank Accession No. JX195664) and Ma-PSY2a (GenBank Accession No. JX195665). Putative transcription initiation (t) and polyadenylation (*) sites are marked on the 5’ and 3’ UTRs (grey arrows), respectively. (b) Analysis of genomic sequences of Asupina and Cavendish PSY genes. Diagrammatic representation of the structure of the genomic sequences corresponding to the coding region (between the start and stop codons) of Asupina and Cavendish PSY genes A-PSY1 (GenBank Accession No. JX195661), A-PSY2a (GenBank Accession No. JX195660), Ma-PSY1 (GenBank Accession No. JX195663) and Ma-PSY2a (GenBank Accession No. JX195662) compared to that of maize (Zm) PSY1 (GenBank Accession No. AY324431.1) and PSY2 (GenBank Accession No. AY325302.1) showing the positions of the exons (black arrows) and introns (grey lines). The sizes (bp) of the exons (bold numbers) and introns (plain numbers) are shown above and below the coding region of each gene (JPEG 768 kb)

Copyright information

© Springer-Verlag 2012

Authors and Affiliations

  • Bulukani Mlalazi
    • 1
  • Ralf Welsch
    • 2
  • Priver Namanya
    • 1
    • 3
  • Harjeet Khanna
    • 1
  • R. Jason Geijskes
    • 1
  • Mark D. Harrison
    • 1
  • Rob Harding
    • 1
  • James L. Dale
    • 1
  • Marion Bateson
    • 1
  1. 1.Centre for Tropical Crops and BiocommoditiesQueensland University of TechnologyBrisbaneAustralia
  2. 2.Faculty of BiologyUniversity of FreiburgFreiburgGermany
  3. 3.National Agricultural Research Laboratories-KawandaKampalaUganda

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