Fig. 1 Generalized pathway leading to anthocyanidin 3-glucosides (Holton and Cornish 1995). Anthocyanins of non-blue flowers (rose, chrysanthemum and carnation) and blue flowers (gentian and petunia) are also shown. Blue flowers usually have delphinidin modified with one or more aromatic acyl group(s) such as caffeic acid (Caf) and coumaric acid. PAL, phenylalanine ammonia-lyase; C4H, cinnamate4-hydroxylase; 4CL, 4-coumarate:CoA ligase; CHS, chalcone synthase; CHI, chalcone isomerase; F3H, flavanone 3-hydroxylase;Fill, flavonoid-3'-hydroxylase; F3'5"H, flavonoid 3\5'-hydroxylase; DFR, dihydroflavonol 4-reductase; ANS, anthocyanidin synthase;3GT, flavonoid 3-glucosyl transferase; CC3H, 4-coumaroyl-CoA 3-hydroxylase; FNS, flavone synthase; FLS, flavonol synthase;Glc, glucose; Rha, rhamnose.

- Chalcone synthase- Antisense RNA approach- Suppression observed with a sense gene introduced

Figure 1. Phenotypes of Chimeric CHS Transgenotes and Variations among Flowers on Single Plants.

- Dr. R. Goldberg (UCLA) and Plant Genetic Systems- Male Sterility- TA29, TA13 genes- Tapetum-specific promoters- RNase gene (Barnase)- Barstar inactivates Barnase- Pollenless

Identity (동질성 ) vs. Variety (다양성 )

-Dioecy, poplar-Monoecy, corn-Heteromorphic flower, flax-Homomorphic flower : SSI, GSI

Brassica, turnips, rape, cabbage, broccoli, and cauliflower.

Sporophytic Self-Incompatibility (SSI)

In this SSI system,

•Rejection of self pollen is controlled by the diploid genotype of the sporophyte generation.

•The control lies in the "S-locus", which is actually a cluster of three tightly-linked loci:

•SLG (S-Locus Glycoprotein) which encodes part of a receptor present in the cell wall of the stigma; •SRK (S-Receptor Kinase), which encodes the other part of the receptor. Kinases attach phosphate groups to other proteins. SRK is transmembrane protein embedded in the plasma membrane of the stigma cell. •SCR (S-locus Cysteine-Rich protein), which encodes a soluble, secreted ligand for the same receptor.

•Because the plants cannot fertilize themselves, they tend to be heterozygous; that is, carry a pair of different S loci (here designated S1 and S

2).

However, dozens of different S alleles may be present in the population of the species; that is; the S-locus in the species is extremely polymorphic (analogous to the major histocompatibility locus of vertebrates — Link).

The difference between the alleles is concentrated in certain "hypervariable regions" of the receptor (analogous to the hypervariable regions that provide the great binding diversity of antibodies — Link). The rules:

Pollen will not germinate on the stigma (diploid) of a flower that contains either of the two alleles in the sporophyte parent that produced the pollen. This holds true even though each pollen grain — being haploid — contains only one of the alleles.

In the example shown here, the S2 pollen, which was produced by a S1S2 parent, cannot germinate on an S1S3 stigma.

Gametophytic Self-Incompatibility (GSI)

Solanaceae, potatoes, tomatoes, and tobacco beets (Beta vulgaris) buttercups (Ranunculus) lilies roses many grasses

This appears to be the mechanism in tobacco:

All pollen grains — incompatible as well as compatible — germinate forming pollen tubes that begin to grow down the style. However, growth of incompatible pollen tubes stops in the style while compatible tubes go on to fertilize the egg in the ovary.

The block within incompatible pollen tubes is created by an S-locus-encoded ribonuclease (RNase), which is synthesized within the style; enters the pollen tube and destroys its RNA molecules

halting pollen tube growth.

The RNase molecules contain a hypervariable region which is the basis for each S specificity (S1, S2, S3, etc.).

The pollen tube expresses a molecule that binds RNase. This targeting molecule also exists is different S specificities (S1, S2, S3, etc.).

In compatible ("nonself") tubes, the targeting molecule sequesters the RNase in a vacuole thus permitting RNAs in the cytosol to survive and growth to continue.

In incompatible ("self") tubes the binding of, for example, the S1 targeting molecule to an S1 binding site on the S1 RNase releases the RNase into the cytosol so the RNAs of the pollen tube are destroyed and growth is halted.

Other mechanisms may be used by other species with gametophytic self-incompatibility.