Transgenic tobacco overexpressing Brassica juncea HMG-CoA synthase 1 shows increased plant growth, pod size and seed yield

PLoS One. 2014 May 21;9(5):e98264. doi: 10.1371/journal.pone.0098264. eCollection 2014.

Abstract

Seeds are very important not only in the life cycle of the plant but they represent food sources for man and animals. We report herein a mutant of 3-hydroxy-3-methylglutaryl-coenzyme A synthase (HMGS), the second enzyme in the mevalonate (MVA) pathway that can improve seed yield when overexpressed in a phylogenetically distant species. In Brassica juncea, the characterisation of four isogenes encoding HMGS has been previously reported. Enzyme kinetics on recombinant wild-type (wt) and mutant BjHMGS1 had revealed that S359A displayed a 10-fold higher enzyme activity. The overexpression of wt and mutant (S359A) BjHMGS1 in Arabidopsis had up-regulated several genes in sterol biosynthesis, increasing sterol content. To quickly assess the effects of BjHMGS1 overexpression in a phylogenetically more distant species beyond the Brassicaceae, wt and mutant (S359A) BjHMGS1 were expressed in tobacco (Nicotiana tabacum L. cv. Xanthi) of the family Solanaceae. New observations on tobacco OEs not previously reported for Arabidopsis OEs included: (i) phenotypic changes in enhanced plant growth, pod size and seed yield (more significant in OE-S359A than OE-wtBjHMGS1) in comparison to vector-transformed tobacco, (ii) higher NtSQS expression and sterol content in OE-S359A than OE-wtBjHMGS1 corresponding to greater increase in growth and seed yield, and (iii) induction of NtIPPI2 and NtGGPPS2 and downregulation of NtIPPI1, NtGGPPS1, NtGGPPS3 and NtGGPPS4. Resembling Arabidopsis HMGS-OEs, tobacco HMGS-OEs displayed an enhanced expression of NtHMGR1, NtSMT1-2, NtSMT2-1, NtSMT2-2 and NtCYP85A1. Overall, increased growth, pod size and seed yield in tobacco HMGS-OEs were attributed to the up-regulation of native NtHMGR1, NtIPPI2, NtSQS, NtSMT1-2, NtSMT2-1, NtSMT2-2 and NtCYP85A1. Hence, S359A has potential in agriculture not only in improving phytosterol content but also seed yield, which may be desirable in food crops. This work further demonstrates HMGS function in plant reproduction that is reminiscent to reduced fertility of hmgs RNAi lines in let-7 mutants of Caenorhabditis elegans.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Arabidopsis / genetics
  • Gene Expression Regulation, Plant
  • Hydroxymethylglutaryl-CoA Synthase / biosynthesis*
  • Hydroxymethylglutaryl-CoA Synthase / genetics
  • Mustard Plant / enzymology*
  • Mustard Plant / genetics
  • Mutation
  • Nicotiana / genetics
  • Nicotiana / growth & development*
  • Phenotype
  • Phylogeny
  • Phytosterols / chemistry
  • Plants, Genetically Modified / genetics
  • Plants, Genetically Modified / growth & development
  • Polymerase Chain Reaction
  • RNA Interference
  • Seeds / growth & development*

Substances

  • Phytosterols
  • Hydroxymethylglutaryl-CoA Synthase

Grants and funding

This work was supported by the Wilson and Amelia Wong Endowment Fund and the University of Hong Kong (CRCG 10400945, CRCG 104001061, University Postgraduate Fellowship (PL) and studentships (HW and ASH)). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.