Compromisos de optimización de diferentes modos de transmisión en un virus de plantas

Plant viruses are important crop pathogens that cause huge loses in agricultural production and may also reduce ecosystem biodiversity by affecting the fitness of wild plants. One of the most important traits determining the extent and severity of plant virus epidemics is their transmission mode and efficiency. The two main modes of plant virus transmission are horizontally from-plant-to-plant, mainly through insect vectors, and vertically from-parents-to-offspring through seeds. Despite the importance of plant virus transmission, little is known on the genetic determinants of this process, particularly for vertical transmission, and on how plant viruses optimize them. One of the most accepted theories on this regard is the Continuum Hypothesis, which poses that the preferred transmission mode would depend on the pathogen virulence and multiplication level: vertically transmitted parasites would evolve towards lower virulence and multiplication, as they require the host to produce progeny to be transmitted, whereas horizontally transmitted pathogens would evolve towards higher virulence and multiplication, which would ensure short-term dispersal through vectors. This theory assumes that both transmission modes will have the same genetic control through virulence and multiplication determinants, and therefore cannot be simultaneously optimized. However, this hypothesis has been seldom experimentally tested. Moreover, whether the genetic determinants of both transmission modes are the same or not is currently unknown. The goal of this Bachelor Thesis is to experimentally test the Continuum Hypothesis, and to explore whether vertical and horizontal transmission have the same genetic determinants. To do so, seven Arabidopsis thaliana accessions were challenged with four different turnip mosaic virus (TuMV) genotypes mutated in domains known to control horizontal transmission such that this capacity is blocked, plus the wildtype. Then, multiplication, virulence and both vertical and horizontal transmission rates were quantified. The results show lesser or equal vertical transmission rate in the TuMV mutants than in the wildtype. Interestingly, mutants with lower vertical transmission rate tended to have lower multiplication and virulence, suggesting a positive correlation between these two traits and vertical transmission rate. These findings: (i) do not support for the Continuum Hypothesis, showing that multiplication and virulence promotes vertical and horizontal transmission in the same way; and (ii) provide evidence that the two transmission modes may share some common genetic determinants