Analysis of the ASR and LP3 homologous gene families reveal positive selection acting on LP3-3 gene.

Drought has long been established as a major environmental stress for plants which have in turn developed several coping strategies, ranging from physiological to molecular mechanisms. LP3 that was first discovered in loblolly pine (Pinus taeda L.) is a homolog of the Abscisic Acid, Stress and Ripening (ASR) gene belonging to the ABA/WDS gene family that was first detected in tomato. LP3 has been shown to be present in four different paralogs in loblolly pine called LP3-0, LP3-1, LP3-2 and LP3-3. LP3 in loblolly pine has not been as extensively studied as the ASR in tomato. Similar to ASR, the different LP3 paralogs have been shown to be upregulated in response to water deficit stress and to act as transcription factors for genes likely involved in hexose transport. In the current study, we have investigated the evolutionary history of LP3 gene family, with the aim of relating it to that of ASR from a phylogenetic perspective and comparing the differences in selective pressure and codon usage. Phylogenetic trees revealed that LP3 is less divergent across species than ASR even when the trees were solely based on the different sub-sections of the gene. Phylogenetic, GC content, codon usage and selective pressure analyses suggest that LP3-3 is undergoing positive selection.