Nanning, Jan. 17-22, 2016
Altered Phenylpropanoid Metabolism in the Maize Lc-Expressed Sweet Potato Affects Storage Root Development Peng Zhang SIBS-ETH Shanghai Center for Cassava Biotechnology Institute of Plant Physiology & Ecology, SIBS, Chinese Academy of Sciences
www.cassavabiotech.org
2 400 million metric tonnes VS VS
800 million metric tonnes Roots & Tubers
Economic Values of Sweetpotato 甘薯 Sweetpotato (Ipomoea batatas Lam.) China is the biggest producer in the world, accounting for more than 50% of harvest areas and 80% production (100 million tons/year); it is mainly used as raw materials for starch, feed and bioethanol.
2 M
⽢甘薯
100 Million
50 Million
Production（MT)
Production（Int $1000)
4 million
“Traditional crops for food security and biomass-based energy”
How sweetpotato adapts to unfavorable environments?
How sweetpotato develops its storage root and accumulates starch?
The Root System of Sweetpotato 30 days
50 days
Fibrous root
Storage root
Pencil root
Ernst Artschwager, Ph.D. 1889-1957
Artschwager, E. (1924) On the anatomy of the sweet potato root with notes on internal breakdown. Jour. Agri. Res., 27: 157–166. McCormick, F.A. (1916) Notes on the Anatomy of the Young Tuber of Ipomoea batatas Lam Botanical Gazette 61(5): 388-398.
Different Biological Processes of Seed Maturation and Storage Root Development Seed Maturation Programme
A Process Largely unknown AC LC RVC RVC
The balance between lignification and cambial cells development during sweetpotato storage root formation
(Vicente-Carbajosa & Carbonero, 2005, Int J Dev Biol 49: 645)
(Firon et al., BMC Genomics, 2013, 14: 460)
Secondary growth of vascular bundles during storage root formation
Determination of secondary growth in vascular bundle
Regulation of secondary growth in vascular bundle
Differentiation of vascular cambium
Cell wall thickening (woods) Special parenchyma cells (storage roots)
The material base of cell growth Transcription factors Signal molecules (hormone etc.)
Question：Photo-assimilate partitioning on storage root development (Competition of primary metabolites)？ Coordination between lignin deposition and starch accumulation?
Transcriptional profiling of sweetpotato (Ipomoea batatas) roots indicates down-regulation of lignin biosynthesis and up-regulation of starch biosynthesis at an early stage of storage root formation
Firon et al. BMC Genomics 2013, 14:460
☺
Lc Promotes Anthocyanin Accumulation in SP Maize MYC-type transcription factor leaf colour (Lc) genes (GenBank: M26227), a protein with the basic-helix-loophelix (bHLH) motif. CaMV 35S
Lc
Nos!
Lc Expression Levels
Developing storage root (S16), stem and leaf of 2-month-old plants
Increased Accumulation of Anthocyanins and Flavonols in Lc Transgenic Lines 花青素
黄酮醇(斛皮素）
Leaves, stems and developing storage roots (S16) of 2-month-old plants
Lc Promotes Flavonoid Biosynthesis in SP
PAL, phenylalanine ammonia lyase; CHI, chalcone isomerase; CHS, chalcone synthase; F3H, flavanone 3-hydroxylase; FLS, flavonol synthase; DFR, dihydroflavonol 4-reductase; ANS, anthocyanidin synthase; 3GT, UDP-glucose:flavonoid 3-O-glucosyltransferase.
G-box binding activity by the yeast one hybrid assay
The Lc-binding element G-box and MYC consensus in the promoter regions of sweet potato anthocyanin and lignin biosynthetic genes
Lc3
WT
Lc2
Lc1
WT
Phenotypic Change of SR in Lc Transgenic SP Lines WT
Lc1
Lc2
Lc3
Mature storage roots (>S18) of 5-month-old plants in field
No Changes in the Photosynthesis Capacity of the Leaves in Lc Lines
Chlorophyll fluorescence
Maximal quantum yield of PSII (Fv/Fm)
Lc Up-regulates the Lignin Biosynthesis Pathway
C4H, cinnamic acid 4hydroxylase; 4CL, 4-coumarate-CoA ligase; CCR, hydroxycinnamoyl-CoA reductase; CAD, cinnamyl alcohol dehydrogenase; COMT, caffeic acid/5hydroxyferulic acid Omethyltransferase. CCoAOMT, caffeoyl-CoA Omethyltransferase;
Leaves, stems, fibrous roots (S5-S8) and developing storage roots (S16) of 2-month-old plants.
Increased Lignin Content in the Root System of Lc Transgenic Lines
Fibrous roots (S5-S8), developing storage roots (S10) and mature storage roots (>S18) of 5-month-old field-grown plants.
Lignin Deposition Patterns in Different Roots
P-H, phloroglucinol-HCl; TB, toluidine blue
Enhanced Starch Metabolism Promoted by Starch Degradation but Not by Starch Synthesis
Enhanced Starch Metabolism Promoted by Starch Degradation but Not by Starch Synthesis
Reduced Starch Accumulation in Lc Transgenic SP
Reduced Sugar Contents in Lc Transgenic SPs
Regulatory Model of Storage Root Development Related to Starch and Lignin Metabolisms in SRs
Starch biosynthesis
Leaf starch metabolism
Starch metabolism
Starch content Starch degradation
？
Glucose
root
Flavonoid biosynthesis
Development
Lc Source
Storage
Lignin biosynthesis
Lignification
Sink
Wang et al. (2016) Scientific Reports 6: 18645.
Transcriptional regulatory network around VNS proteins, first-layer master switches for secondary cell wall formation, based on work in Arabidopsis.
Nakano Y, Yamaguchi M, Endo H, Rejab NA and Ohtani M (2015) NAC-MYBbased transcriptional regulation of secondary cell wall biosynthesis in land plants. Front. Plant Sci. 6:288.
Regulatory model of IbNAC83 (VNI2 homolog) during SR development IbNAI17(VND7)
Ø A cause-and-effect relationship between increased lignification and reduced storage root yield. Ø Lignification competes with starch accumulation for the distribution of photo-assimilates in developing storage roots. Ø Both primary and secondary metabolisms play important roles in regulating the carbon partitioning between “Source” and “Sink”. Ø Important regulators that maintain the storage cell expansion and storage starch accumulation in developing storage roots are required to be disclosed.
Acknowledgements Hongxia Wang, Ph.D. Jun Yang, Ph.D. Weijuan Fan, Ph.D. Yinliang Wu Min Zhang Laigeng Li, Prof.
Funding supports: 科技部 MOST 国家自然基金委 NSFC
Collaborators: Nurit Firon, Ph.D., ARO, Israel Ling Yuan, University of Kentucky, USA
phloroglucinol-HCl (P-H)
toluidine blue (TB)
AUX1, auxin transporter protein 1; PIN1a, PIN-FORMED1a; PIN1b, PIN-FORMED1b.
Thank you
