AUTHOR=Sun Lina , Wang Huaxin , Li Jinhua , Gong Jianying , Yang Shuting , Yang Kaitai , Chen Er , Li Bing , Lu Zhixiang , Chen Qi , Lin Mao 

TITLE=Mechanistic analysis of the hardening process of the thorns on stems of Bougainvillea glabra “Elizabeth Angus”

JOURNAL=Frontiers in Genetics

VOLUME=15

YEAR=2024

URL=https://www.frontiersin.org/journals/genetics/articles/10.3389/fgene.2024.1375488

DOI=10.3389/fgene.2024.1375488

ISSN=1664-8021

ABSTRACT=<p><bold>Introduction:</bold><italic>Bougainvillea glabra</italic> “<italic>Elizabeth Angus</italic>“ is a thorny woody vine or shrub. However, the hard thorns are considered a deficiency in its ornamental value.</p><p><bold>Methods:</bold> To find the genes and pathways related to the hardening process of the thorns on the stems of <italic>B. glabra</italic>, the eukaryotic unreferenced transcriptome sequencing analysis was conducted to explore the 3 stages of the thorn-hardening process. Total RNA was extracted from thorns and stems, and transcriptome libraries were constructed and sequenced using unreferenced Illumina sequencing.</p><p><bold>Results:</bold> Gene function annotation was performed using various databases, resulting in 8937 co-annotated genes. The density distribution of Fragments Per Kilobase of transcript per Million mapped reads (FPKM) depicted the overall gene expression patterns. The study found that stage 2 as the period of highest gene expression activity during the thorns hardening process in <italic>B. glabra</italic>. Differential expression analysis revealed that during thorn-hardening, 1045 genes up-regulated and 391 genes down-regulated significantly in thorns at stage 2 compared to stage 1 (early stage of thorns formation). Meanwhile, 938 genes up-regulated and 784 genes down-regulated significantly in stems. At stage 3, as thorns became harder, 63 genes exhibited notable expression increase and 98 genes’ expression decreased obviously within thorns, and 46 genes up-regulated and 29 genes down-regulated in stems, compared to stage 2. Phenylpropanoid biosynthesis was the key step in the hardening process of the thorns of <italic>B. glabra</italic>. The formation and hardening of thorns on the stem of <italic>B. glabra</italic> was a process in which lignin gradually accumulated in the thorns, and several genes were involved in this process. They include <italic>PAL</italic> (EC:4.3.1.24), <italic>CYP73A</italic> (EC:1.14.14.91), <italic>4CL</italic> (EC:6.2.1.12), <italic>CCR</italic> (EC:1.2.1.44), <italic>CAD</italic> (EC:1.1.1.195) and <italic>POX</italic> (EC:1.11.1.7).</p><p><bold>Discussion:</bold> This transcriptome analysis offers insights into the molecular mechanisms underlying thorns development in this plant species.</p>