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Cryptic self-incompatibility of flowers

By Seolncr Subscribe to RSS | January 31st 2012 | Views:

There is evidence, for example, Silene vulgaris ( Caryophyllaceae ),Amsinckia grandiflora ( Boraginaceae ), Decodon verticillatus ( Lythraceae ) and Cheiranthus cheiri ( Brassicaceae ) have this mechanism. In this type of self-incompatibility, the simultaneous presence in the stigma of foreign pollen and pollen from the same plant results in a greater number of progeny from pollination with foreign pollen.

However, and contrary to what happens to the self-incompatibility "complete" or "absolute" described previously, the AIC can be no fertilization and seed production in the absence of foreign pollen. This ensures the reproduction of the individual even if it is isolated from another individual of the same species. The AIC acts, at least in some of the species studied, at the stage of elongation of pollen tubes within the pistils and leads to an elongation rate of growth or higher in pollen tubes from foreign pollen, which arrive in the make eggs and fertilization of the oosphere before the pollen tubes from the pollen of the plant. The cellular mechanisms and molecular determinants of the AIC have not been described until April 2008.The strength of AIC's response can be defined as the ratio between the number of oosphere fertilized by foreign pollen on the number of oosphere fertilized by pollen from the plant itself when applying the same amount of foreign pollen as characteristic of the plant on the stigmas of the same. This relationship goes from 3.2 to 11.5 in the taxa studied so far.

Wild species of tomato ( Solanum lycopersicum ) is differentiated by its mode of reproduction. Thus, species AI and, therefore, are "cross-pollinated." On the other hand, there are self-pollinating species and is usually self-fertilizing, are said to be self-compatible (AC) and, therefore, self-pollinating. In between, finally, there are species with AI and AC populations, and others that are usually AI but can give a proportion of selfed seeds (optional pollinated are called).

The degree to which the stigmata are elongated above the stamens (variable called " protrusion of the stigmas ") is a central factor in the possibility of cross-pollination and, hence, of outcrossing in these species. Related species tomato are required or optional AI have flowers with very protruding stigmas. In contrast, other species such as the cultivated tomato, inserted stigmas present which promotes self-pollination. It was observed that a region of the genome of tomato (oneQTL , English acronym to designate a locus that determines or governs a quantitative trait) is responsible for a large proportion of the phenotypic variability observed for this character and that mutations in this locus are involved in the evolution from outcrossing to autogamy in this species. The location of this QTL in the tomato genome has led to the conclusion that is a locus complex comprising at least 5 genes closely linked, one that controls the length of style, 3 that control the size of the stamens and the last that governs anther dehiscence. This group of genes represent the remains of an ancient complex of co-adapted genes that control mating type in these species of Solanum .

In 2007 it has gone a step further in understanding this group of genes because it has determined the base sequence of the locus , the gene responsible for the length of the style. This gene encodes a transcription factor that regulates cell elongation in developing styles. The transition from AI to CA was accompanied only by a change in the protein by a mutation in the promoter of the gene resulting decrease in the expression of this gene during floral development and therefore the consequent shortening of the length of the styles.

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