Evolutionary History, Transcriptome Expression Profiles, and Abiotic Stress Responses of the SBP Family Genes in the...

Squamosa promoter binding protein (SBP) plays a vital role in plant growth, development, and responses to abiotic stresses. The genus Notopterygium is an endangered perennial herbaceous plant mainly distributed in the high-altitude Qinghai-Tibet Plateau and adjacent areas, which possibly occurred the adaptive evolution to the extreme environmental conditions. In this study, we firstly determined the genome-wide structural characteristics, evolutionary history, and expression profiles of the SBP family genes in Notopterygium species by using genome, transcriptome, and DNA resequencing data. We have also investigated the response patterns of SBPs of N. franchetii to the drought and high-temperature stresses. The 21, 18, and 18 SBP family genes of three Notopterygium species, N. incisum, N. franchetii, and N. forrestii, were, respectively, identified and classified into eight subfamilies, with four subfamily members regulated by miR156. The structure analysis showed that the members of the same SBP subfamily had similar structures and conserved motif composition. Cis-element analysis suggested that those SBP genes may have been essential to the growth and environmental adaptation of Notopterygium. The expansion of the SBP gene family was mainly caused by the whole genome duplication/segmental duplication and transposable element duplication. Evolutionary analysis showed the SBP gene family experienced severe contraction events and most of the gene copies underwent purification selection. Population genetics analysis based on SBPs variations suggested that the genus Notopterygium species have obvious genetic structure and interspecific differentiation. RNA-seq and qRT-PCR experiments demonstrated that the expressions of SBPs genes in Notopterygium were not species-specific, but tissue-specific. NinSBP08 and NinSBP10/12 may have played the key roles in heat tolerance and drought resistance, respectively. These results provided novel insights into the evolutionary history of the SBP gene family in the endangered herb Notopterygium species in the high-altitude Qinghai-Tibet Plateau and adjacent areas.