Abstract
Survival in harsh environments is associated with several adaptations in plants. Species in the Portulacineae (Caryophyllales) have adapted to some of the most extreme terrestrial conditions on Earth, including extreme heat, cold, and salinity. Here, we generated 52 new transcriptomes and combined these with 30 previously generated transcriptomes, forming a dataset containing 68 species of Portulacinaeae, seven from its sister clade Molluginaceae, and seven outgroups. We performed a phylotranscriptomic analysis to examine patterns of molecular evolution within the Portulacineae. Our inferred species tree topology was largely congruent with previous analyses. We also identified several nodes that were characterized by excessive gene tree conflict and examined the potential influence of outlying genes. We identified gene duplications throughout the Portulacineae, and found corroborating evidence for previously identified paleopolyploidy events along with one newly identified event associated with the family Didiereaceae. Gene family expansion within Portulacineae was associated with genes previously identified as important for survival in extreme conditions, indicating possible molecular correlates of niche changes that should be explored further. Some of these genes also showed some evidence for positive selection. The correlation between gene function and expansion suggests that gene/genome duplication have likely contributed to the extreme adaptations seen in the Portulacineae.
