Although considerable effort has been invested in describing the phenotypic traits required for invasiveness, little is known
about their genetic basis. However, as a result of the technological revolution in (functional) genomics, this situation is
rapidly changing. Importantly, it has brought molecular genetics within the reach of ecologists, since gene-expression profiling,
also called transcript profiling, has become technically feasible even in less well-equipped laboratories. In addition, the
frequent use of transcript profiling has lowered its cost and increased the possibility of outsourcing analyses. Nowadays,
most laboratories are capable of identifying genes of interest and of monitoring either their individual expression via quantitative
PCR or RNA gel-blots or their simultaneous expression using microarrays and high-throughput quantitative transcriptome sequencing.
These advances have allowed the ‘ask-the-plant’ experimental approach to be implemented on a genome-wide, and thus unbiased,
scale. Moreover, our increased grip on how such candidate genes can be manipulated, via forward and reverse genetics, allowed
for assessing the function of alleged ‘plant competition genes’ efficiently. In this chapter we will focus on the molecular
mechanisms underlying plant competition, especially those identified through transcript analysis, and discuss how modern molecular
tools have illuminated our understanding of the genetic basis of the dynamic and variable ecological phenomenon of invasiveness.