Genomic Analysis and Expression Investigation of Steroleosin Gene Family in Arabidopsis Thaliana

Abstract

Despite having growing evidence discussing the role of steroleosins in crop plants, their systemic analysis has not been worked extensively. Therefore, bioinformatics tools were employed to study Arabidopsis (Arabidopsis thaliana) steroleosin in comparison with reported Brassica napus and pine steroleosins. Based on molecular weight, eight steroleosins in Arabidopsis were divided into two groups, L-steroleosin (alkalescence) and H-steroleosin (acidity except At5g50770). Phylogeny analysis suggested that H-steroleosins in Arabidopsis are primitive. Moreover, phylogeny, protein alignment, motif analysis and gene structure analysis revealed that the reported steroleosins in B. napus are closely related to H-steroleosins. Similarly, Gene structure analysis revealed an insertion of 10 residues at the C-terminal of H-steroleosin which makes it relatively larger as compared to L-steroleosins. According to the Protein-protein interactions, Arabidopsis steroleosins are interrelated with genes involved in fatty acid biosynthesis and stress tolerance. Duplication studies suggest that among the steroleosin genes in Arabidopsis, segmental duplications are newly developed. Expression analysis suggests that H-steroleosins mainly express in seed tissue, while L-steroleosins diverge in two directions: expression or repression in all tissues. The upstream sequence analysis suggests that Arabidopsis steroleosins are involved in lipid metabolism and the brassinosteroid signaling pathways. The roles of steroleosins for stress responses are indicated by their induced expression under stress and abscisic acid treatments. Therefore, further investigations are required to evaluate the functions of steroleosins in plants.

Genome-wide analysis revealed the stepwise origin and functional diversification of HSDs from lower to higher plant species

“…DNA segments that are nearly identical (90%-100%) and found on multiple genomic sites are referred to as segmental duplications (Khaja et al, 2006). Previous studies suggest that within Arabidopsis, AtHSD1a and AtHSD4a are found to be segments of AtHSD1b and AtHSD4b, respectively, which is due to the 33-kb duplication events on chromosome 5 (Baud et al, 2009;Aziz et al, 2020). Our study revealed that both segmental and tandem duplication were the reasons for HSD1s in plants.…”

“…Expression analysis of two HSD genes, HSD1 and HSD5, shows that they are predominantly upregulated in seeds, which are the essential site for TAG assembly and are considered to provide energy for developing seeds. Thus, the high expression level of two HSDs in seeds provides more evidence for their involvement in triacylglycerol metabolism (Aziz et al, 2020). Fascinating to notice, A. hypochondriacus HSD1 and HSD5 are mainly upregulated in floral and seed tissues, while the maximum expression level of G. max HSD1 and HSD5a and b was only noticed in seed tissues (Table S3).…”

“…According to physiochemical studies, except for HSD5, all the other HSDs were mainly basic in nature (Table 4). These results collectively suggest that steroleosins may have diversified roles within plant species (Aziz et al, 2020). According to the upstream sequence analyses, the majority of the HSDs within different plant species have a cis-element such as lightresponsive element (G-Box), a TATA-box, an RY-element, and a DRE core.…”

“…To date, eight HSD proteins have been identified in the TAIR genome (Lin et al, 2002;Li et al, 2007;Baud et al, 2009). Among the identified HSDs, two are homologous to AtHSD1 (At5g50600 and At5g50700) and AtHSD4 (At5g50590 and At5g50690) (Aziz et al, 2020). Therefore, in the current analysis, one protein sequence from each homologue was used to identify the respective HSDs (HSD1 and HSD4) in other plant species.…”

“…This suggests that HSD1 in plants may have been the first to evolve (Figure 1 and Table 1). The HSD5s were limited to land plants (Table S1B) and in P. massoniana, which is a relatively old gymnosperm (Aziz et al, 2020). It is worth noting that no HSD was found in other gymnosperms, suggesting that HSD5 was only evolved in the pine genome and later lost in other gymnosperms.…”