Genes Involved in Biosynthesis Secretion and Release of Seed Coat Mucilage of Myxospermy

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1 ISSN CN / Q http / / cjbmb bjmu edu cn Chinese Journal of Biochemistry and Molecular Biology ~ 124 * Q78 Genes Involved in Biosynthesis Secretion and Release of Seed Coat Mucilage of Myxospermy YUAN Jun-Wen LAN Hai-Yan * Xinjiang Key Laboratory of Biological Resources and Genetic Engineering College of Life Science and Technology Xinjiang University Urumqi China Abstract Seed coat mucilage consists of pectin polysaccharides secreted by the Golgi apparatus in epidermal cells to the cell cavity and cell walls of the seed coat The striking feature of the myxospermy is formation of a gelatin-like capsule mucilage around the seed upon contact with water which is believed to help with seed hydration ecologically advantageous for seed dispersal germination seedling survival and establishment The molecular mechanism of mucilage synthesis and its novel system to dissect cell wall production are important to study the relationship between seed coat and complex environment In the present review we intend to introduce the latest results achieved in the model plant Arabidopsis thaliana with the mucilage secretory cells MSCs differentiation and its regulatory genes in the process of seed coat mucilage biosynthesis secretion and release Consequently the expected direction in this research area is prospected and discussed we hope to stimulate research in both theory and application of myxospermy plant species and to provide convincing evidence for protection of biodiversity and utilization of biological resources in the desert region of northwest China Key words Arabidopsis thaliana myxospermy seed coat mucilage mucilage secretory cells gene mutant No No XJDX * Tel lanhaiyan@ xju edu cn myxospermy Received September Accepted December Supported by National Natural Science Foundation of China No and Open Foundation of Xinjiang Key Laboratory of Biological Resources and Genetic Engineering No XJDX * Corresponding author Tel lanhaiyan@ xju edu cn

2 ~ 3 8 Cruciferae Plantaginaceae Asteraceae Linaceae Fig 1 Brassica Cydonia Ruellia Plantago TTG1 Tranparent testa glabra 2 TTG2 Tranparent testa 8 TT8 Myeloblastosis MYBs Capsella bursa-pastoris Sinapis alba / Brassica alba Lunaria annua S alba Brassica campestris Lepidium sativum L Lesquerella fendleri 4 Raphanus sativus 5 Apetala 2 AP2 Tranparent testa glabra 1 Arabidopsis thaliana Fig 1 Development of the mucilage secretory cells MSCs Micrographs of toluidine blue stained MSCs at different stages of differentiation The diagram to right and captions to the left indicate phases of differentiation 1 mucilage secretory cells MSCs cytoplasm 2 vacuole 3 mucilage 4 cell wall columella Pollination triggers cell growth by vacuolar expansion Mucilage production becomes apparent in toluidine blue stained sections as pink accumulation in the cells Upon 1 the completion of mucilage synthesis and secretion a cytoplasmic column is found in the centre of the cell with mucilage on either side Secondary cell wall deposition 6 2 ~ 5 surrounding the cytoplasm eventually fills in the centre of the cell The remaining cytoplasm at the base of the cell undergoes 7 8 death and dehydration of the seed reveals the contour of the 6 secondary cell wall Apetala2 AP2 AP2 AP2 euap2

3 Tranparent testa 8 TT8 1 α- 1 3 β DNA 16 bhlh TT AP2 / EREBP 17 TTG1 TT2 18 ap2 TT8 ap2-6 egl3 enhancer of glabra 3 gl3egl3 glabra3 - enhancer of glabra 3 tt8 egl3 tt8 gl3 egl3 4d TT8 EGL Tranparent testa glabra 1 TTG1 TTG1 WD40 WD40 AtMYB5 TT TTG1 - Gly-His Trp- TT2 21 Asp WD WD40 WD40 AtMYB5 TT8 GL2 TTG2 TTG1 MYB5-TT2 EGL3- TT8 GL2-TTG2 TTG1 13 TTG1 TT2 TT8-MYB5 TTG2 ttg Fig 2 ttg1 TTG1 2 Haughn TTG1 TT2 TT8 TT8 bhlh basic helix-loop-helix 1 3 Tranparent testa glabra 2 TTG2 Fig 2 Proposed model for the regulation of TTG1- TTG2 WRKY WRKY dependent developmental pathways Solid arrows indicate direct regulation of a complex Dashed arrows N WRKYGQK indicate a multi-step differentiation pathway 7 TTG ttg2 15 mucilage

4 2 119 secretory cells MSCs gl d 8 9 MSCs Table 1 AP2 24 Apetala2 NARS1 NAC-regulated seed morphology1 / NAC TTG2-27 MUM4 26 TTG1 TT8 MYB5 MYB23 EGL3 GL2 MYB61 MUM4 / RHM2 Mucilagemodfied4 / RHM2 RSW3 Radial swelling MUM2 MUM3 MUM5 PTY mum4 33 Patchy 24 MUM1 AtSBT AtGA3OX4 Gibberellin 3-oxidase4 ABE1 ABE4 GalUA Rha MUM MUM4 3 1 Glabra2 GL Mucilage-modified4 MUM4 MUM4 NDP-L- mum4 AP2 TTG1 GL2 GL2 Homeobox 3 3 Rhamnose synthase 2 RHM2 HD- RHM2 ZIP Homeodomain-leucine zipper 3 AtRHM1 AtRHM2 AtRHM3 RHM2 MUM4 L- GL2 CAPRICE CPC 33 RHM2 TTG1 GL1 GL2 gl2 RHM2 RHM NDP- NDP- NDP- 34

5 Table 1 Genes involved in differentiation of MSCs in A thaliana Gene Mutant phenotype Protein Role References Regulator of outer integument biosynthesis Apetala2 AP2 No mucilage or columella AP2 TF nars1 nars2 Regulator of seed coat development Transparent testa glabra2 TTG2 Transparent testa 8 TT8 MYB5 Regulator of mucilage synthesis No mucilage or columella Reduced mucilage and columella Reduced mucilage and columella egl3 tt8 double Abnormal testa and columella shape reduced mucilage NARS1and NARS2 WRKY TF bhlh TF Unknown Regulator of outer integument differentiation Regulator of outer integument development Regulator of mucilage synthesis and GL2 expression Regulator of mucilage and seed coat synthesis Regulator of mucilage and seed coat synthesis MYB23 Reduced mucilage and columella MYB TF Regulator of mucilage synthesis 9 Enhancer of glabras EGL3 Reduced mucilage and columella egl3 tt8 double bhlh TF Regulator of mucilage synthesis 30 Glabra2 GL2 Reduced mucilage and columella Homeobox TF Regulator of mucilage synthesis TTG2 Reduced mucilage and columella WRKY TF Regulator of mucilage synthesis 29 MYB61 Reduced mucilage and columella MYB TF Regulator of mucilage synthesis 2 UDP-Lrhamnose Regulator of mucilage synthesis 9 Mucilage-modfied4 Reduced mucilage and columella MUM4 RHM2 synthase Regulator of mucilage release Radial swelling3 RSW3 Reduced mucilage and columella Glucosidase II Pectin biosynthesis MUM1 No mucilage release on hydration Unknown Regulator of mucilage release 24 MUM2 MUM3 Regulator of mucilage modification MUM5 Patchy PTY Aberrant testa shape ATS Gibberelin-3oxidase4 AtGA3OX4 Abscisic acid1 ABA1 Arabidopsis thaliana subtilisin-like serine proteases1 7 AtSBT1 7 ABE1 and ABE4 No mucilage release on hydration Altered and reduced mucilage staining Altered and reduced mucilage staining No mucilage release on hydration Abnormal testa development and reduced mucilage staining Reduced mucilage staining and abnormal columella shape Reduced mucilage staining No mucilage release on hydration Mucilage reduced and faltcolumella Glycosyl hydrolase Primary cell wall or mucilage modification 48 Unknown Pectin modification 24 Pectin methylesterase Glycosyl hydrolase De-esterification of pectins Primary cell wall or mucilage modification Unknown 28 GA-3-oxidase Zeaxanthin epoxidase Subtilisin-like serine protease α / βfold hydrolases / esterases Question mark indicate the precise functions of the gene remains unclear Reduced columella synthesis reduced starch Cell wall disruption on hydration Regulator of mucilage synthesis

6 MYB5 MYB5 R2R3-MYB MUM3 MUM Li T-DNA 4 2 MYB61 25 MYB5 MYB61 R2R3-MYB 38 GC-MS MYB5 GL2 MYB5 MYB61 MYB5 TTG1 / TT8 / EGL3 MYB61 ABE1 ABE4 GL2 MYBL2 GH 3 5 NARS1 / NAC2 NARS1 / NAC2 NAC NAC III MUM1 MUM2 109 NAC GC-MS mum1 mum2 36 Kunieda NARS1 / NAC2 NARS2 / NAM 10 d NARS1 / NAC2 6% ~ 8% NARS1 NAC2 NARS1 NAC2 47 MUM2 nars1nac2 β-d-galactosidase β-d- 25 BGAL6 mum MUM3 MUM5 80% 2 39 PGA I RGI 4 4 Patchy PTY Patchy β- patchy 0 42 nm mum3 mum5 patchy α

7 β- α mor1-1 MYB23 R2R3MYB Radial 4 5 AtSBT1 7 swelling3 RSW3 MUM enhancers Gibberellin-3 AtSBT1 7 subtilisin-like oxidase4 AtGA3OX4 41 ~ 44 serine protease AtSBT1 7 SB S8 AtSBT1 7 ABA 6 ~ 10 d 5 40 AtSBT1 7 pectin methylesterase PME 45 AtSBT1 7 PME AtSBT % 46 ~ 49 Fig 3 The regulatory network model of seed coat epidermal cells & seed coat mucilage development Solid lines indicate interactions between members of a complex Solid arrows indicate direct regulation of a gene References 1 Witztum A Gutterman Y Enenari M Integument mucilage as an oxygen barrier during germination of B epharis persica Burm Kuntze J Bot Gaz J Plant Cell Fig 3 3 Windsor J B Symonds V V Mendenhall J et al integument J Plant J Penfield S Meissner R C Shoue D A et al MYB61 is required for mucilage deposition and extrusion in the Arabidopsis seed coat Arabidopsis seed coat development morphological differentiation of the outer

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