SCN:

SCN Basics

SCN Life Cycle
SCN Life cycle pictures (May require substantial loading time)

SCN Invasion (pictures! May require substantial loading time)
2 day
4 day
6 day
8 day

SCN databases
SCN gene database
SCN genes of interest
Soybean cv SCN race

Soybean Defense Response
Defense Response overview 
Thru the microscope
Thru microarrays
microarray database
Soybean gene database

Hypersensitive response
Oxidative burst
Systemic Acquired Resistance

R genes
R gene overview
Rhg mapping
Rhg1
Rhg4

Pathways
Jasmonic acid
Salicylic acid
Secondary products
Ethylene
Sucrose & Trehalose

Genes/enzymes              peroxidase  
copper amine oxidase

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      Jasmonic acid (JA), is a growth inhibitor, senescence-promoting substance. Jasmonates, such as jasmonic acid, are cyclopentanone derivatives synthesized from linolenic acid via the octadecanoic pathway.  JAs is structurally related to prostaglandins, which are autacoidal hormones found in mammals. JA is synthesized from alpha-linolenic acid, which is a C18 poly-unsaturated fatty acid.  It is synthesized from plant membranes by enzymes similar to lipase.  Key JA biosynthetic enzymes have chloroplast transit peptides that directing their import into the chloroplast.  Key enzymes include lipoxygenase, allene oxide synthase, and allene oxide cyclase.

      JA can be conjugated to amino acids, ie. leucine, valine, isoleucine and the sugar, B-glucoside using UDP-glucose.  (-)-JA and (-)-methyl jasmonate are major JAs in plants.  JA induces vegetative storage proteins, osmotin, thionin (antifungal) and defensin. It induces the phytoalexin-related enzymes chalcone synthase, PAL, and hydroxymethylglutaryl-COA reductase. Induces protease inhibitors to control insects.  JA and ethylene induce PR-3, PR-4, PDF1.2, chitinases (CHI-B), and hevein-like protein.

 12-oxo-phytodienoic acid is also a physiological signal for defense.

Jasmonic Acid biosynthetic pathway  

octadecanoid pathway (end product is JA)

   Phospholipase                       Literature summary       cDNAs for A2, C, D
    Lipoxygenase (adds an oxygen)   Literature summary        cDNAs for 2,3,4,5,7,C
   Allene oxide synthase 1, 2, 3
    Allene oxide cyclase  (Chloroplast)  Literature summary  cDNAs for

     12-oxo-phytodienoic acid reductase – Three isoforms in A. thal.  Only one makes    physiologically active JA.  What do the other two do, because they cannot substitute for the correct isoform encoded by OPR3. OPDA also can serve as a signal for defense (Howe, Stintzi)

Refs:

Howe, G.A. 2001. PNAS 98:12315-19

Klessig, D.F, J. Durner, J. Shah, Y. Yang. 1998. Phytochemical Signals and Plant Microbe Interactions, ed. Romeo et al. Ch. 7. Plenum Press, NY. pp.119-137

Stintzi  et al. 2001.PNAS 98:12837-42