Insights on the adaptation to high altitude from transcriptome profiling:A case study of an endangered species Kingdonia uniflora

Kingdonia uniflora is an alpine endangered herb that is distributed along altitudinal gradient. The unique traits and important phylogenetic position make K. uniflora an ideal model for exploring how endangered plants react to the altitude variation. In this study, we selected three locations ranging from 2300-3300m at Taibai mountain (the highest peak in Qinling mountain) to sample tissues. At each location, we collected three individuals that were isolated from each other at least 5m to represent this populations. This could be viewed as biological replicates within group. For each individual, we sampled two tissues for transcriptome sequencing: leaf and flower bud. All fresh tissues were stored in liquid nitrogen. In all, we obtained 6 groups of tissues: A, B, C (leaf), C, D, E (flower bud), a total of 18 samples for transcriptome sequencing, aiming to address the following two questions: (1) whether the gene expression patterns varied along the altitudinal gradient in K. uniflora, if so, how many and what kind of differentially expressed gens (DEGs); (2) whether different tissues of K. uniflora presented the same gene expression pattern when adapting to high altitude environment. We revealed that genes responded to light stimuli and circadian rhythm genes were significantly enriched DEGs in the leaf tissue group, while genes that were related to root development and peroxidase activity, or involved with pathways of cutin, suberin, wax biosynthesis and monoterpenoid biosynthesis were significantly enriched in DEGs in the flower bud tissue group. All of the above genes might play an important role in the response of K.uniflora to various stresses like low temperature, hypoxia in a high-altitude environment. Furthermore, we proved that the discrepancy of gene expression pattern between leaf and flower bud tissue varied along the altitudinal gradient. Overall, our findings provided new insights into the adaptation of endangered species to high altitude environments and would encourage more parallel reseachers to focus on the molecular mechanism of alpine plants' evolution.