Sexual Reproduction in Flowering Plants

Clonality

Flowering plants possess an unrivalled diversity of mechanisms for achieving sexual and asexual reproduction, often simultaneously. The commonest type of asexual reproduction is clonal growth (vegetative propagation) in which parental genotypes (genets) produce vegetative modules (ramets) that are capable of independent growth, reproduction, and often dispersal. Clonal growth leads to an expansion in the size of genets and increased fitness because large floral displays increase fertility and opportunities for outcrossing. Moreover, the clonal dispersal of vegetative propagules can assist “mate finding,” particularly in aquatic plants.

However, there are ecological circumstances in which functional antagonism between sexual and asexual reproductive modes can negatively affect the fitness of clonal plants. Populations of heterostylous and dioecious species have a small number of mating groups (two or three), which should occur at equal frequency in equilibrium populations. Extensive clonal growth and vegetative dispersal can disrupt the functioning of these sexual polymorphisms, resulting in biased morph ratios and populations with a single mating group, with consequences for fertility and mating. In populations in which clonal propagation predominates, mutations reducing fertility may lead to sexual dysfunction and even the loss of sex. Recent evidence (Go to: SEXUAL DYSFUNCTION, SOMATIC MUTATIONS, AND STERILITY IN CLONAL POPULATIONS) suggests that somatic mutations can play a significant role in influencing fitness in clonal plants and may also help explain the occurrence of genetic diversity in sterile clonal populations. Highly polymorphic genetic markers offer outstanding opportunities for gaining novel insights into functional interactions between sexual and clonal reproduction in flowering plants.

Mads box transcription factors

MADS-box genes encode transcription factors that are involved in developmental control and signal transduction in eukaryotes. In plants, they are associated with numerous development processes. Out of which the most notable are those related to reproductive development: flowering induction, specification of inflorescence and flower meristems, establishment of flower organ identity, as well as regulation of fruit, seed and embryo development. Genomic analyses of MADS-box genes in different plant species are providing new relevant information on the function and evolution of this transcriptional factor family.

 The Arabidopsis genome contains a large family of MADS-box genes (approximately 30 to date have been cloned), and many of these play important roles in flower development. The MADS-box itself is a conserved region found at the 5′ of all plant MADS-box genes. It encodes a DNA-binding domain found in other eukaryotic transcription factors, such as MCM1 from yeast, and SRF found in humans.

This article contains more information about these TFs.

Plant genetic response to climate change

Classical Mendelian inheritance assumes the randomized inheritance of chromosomal genes passed on from parent to offspring. In a diploid plant species, the zygote is derived from the fusion of two haploid gametes, one contributed by its maternal and one by its paternal parent. These gametes were formed after a random segregation during meiosis in each parent. The fertilization of the female (egg) by the male gamete (pollen) is likewise thought to be random. Therefore, when no internal or external factors are operating, the genetic composition of the progeny population can be described with statistical precision by the laws of probability theory. Fundamental principles are regular segregation and independent assortment between different pairs of alleles (Grant 1975). Based on these assumptions a whole body of population and quantitative genetic theory has been developed for plant population changes under the evolutionary forces of natural selection, mutation, migration and drift (i.e. Falconer 1989; Hedrick 1985). The models have been verified in a large set of observational and experimental data.

Analysis of DNA markers in the plants revealed that the climate change treatments had altered the genetic composition of the plant populations. The results also indicated a process of evolutionary change in one of the study species, suggesting that genetic diversity may be able to buffer plants against the harmful effects of climate change, allowing an “evolutionary rescue”

Dr Raj Whitlock, from the University’s Institute of Integrative Biology, said:

“Our understanding of the potential for such responses to climate change is still limited, and there have been very few experimental tests carried out within intact ecosystems. We found that experimental climate change treatments can modify the genetic structure of plant populations within 15 years, which is very fast, in evolutionary terms. Evolutionary flexibility within the plant populations at Buxton may help to explain why the grassland there has proven resistant to simulated environmental change. “Climate change is expected to present a significant challenge to the persistence of many populations of wild plant species.”