In rice, an overrepresentation of genes involved in defense response and apopstosis in eQTLs were observed. Also, a study comparing the genomes of humans and chimpanzees to identify positively selected genes reported an enrichment of immunity, defense and apoptosis related genes among the positively selected genes. Similarly, in fish, genes related to immune response and defense response were overrepresented in the positively selected gene list. This rapid evolution of apoptosis genes could be due to the following reasons. First, many apoptosis genes may be newly evolved genes and thus still evolving rapidly under the action of natural selection. Second, because apoptosis related genes are involved in immune and defense response, these genes are rapidly evolving to adapt to new pathogens as shown in the following examples. Bishop et al. showed an excess of nonsynonymous compared to synonymous rates in plant class I chitinase in the genus Arabis. Plant chitinases confer resistance to diseases by degrading chitin, a component of fungal cell walls. Likewise, in wheat, signatures of diversifying selection were observed at the Pm3 locus, which confers resistance to wheat powdery mildew, through an excess of nonsynonymous to synonymous nucleotide divergence. The genes showing signatures of positive selection in this study could be valuable targets for selecting candidate SNPs for growth and survival traits in a range of Eucalyptus species as consistent results were obtained across two Eucalyptus species. However, results from this study need to be treated cautiously as pooled samples are used for detecting the positive selection signatures. These results need to be verified by sequencing of individual samples. The E2F family of transcription factors consists of nine members with both distinct and overlapping functions. E2F1�C6 form heterodimers with DP proteins to achieve highaffinity DNA binding, while E2F7 and 8 do not require these cofactors to bind to E2F target genes. E2F proteins are situated at the ��bottom�� of the growth factor signaling cascade where they regulate genes involved in cell cycle progression, and can act either as transcriptional activators or repressors depending upon their association with pocket proteins such as pRB.