Insight into the Molecular Evolution of Non-Specific Lipid Transfer Proteins via Comparative Analysis Between Rice and Sorghum

Abstract

Phylogenetic analysis was conducted on 9 kDa non-specific lipid transfer protein (nsLTP) genes from nine plant species. Each of the five classified types in angiosperms exhibited eight conserved cysteine patterns. The most abundant nsLTP genes fell into the type I category, which was particularly enriched in a grass-specific lineage of clade I.1. Six pairs of tandem copies of nsLTP genes on the distal region of rice chromosomes 11 and 12 were well-preserved under concerted evolution, which was not observed in sorghum. The transgenic promoter–reporter assay revealed that both rice and sorghum nsLTP genes of type I displayed a relatively conserved expression feature in the epidermis of growing tissue, supporting its functional roles in cutin synthesis or defence against phytopathogens. For type I, the frequent expression in the stigma and seed are indicative of functional involvement in pistil–pollen interactions and seed development. By way of contrast, several type V genes were observed, mainly in the vascular bundle of the rosette as well as the young shoots, which might be related with vascular tissue differentiation or defence signalling. Compared with sorghum, the highly redundant tissue-specific expression pattern among members of rice nsLTP genes in clade I.1 suggests that concerted evolution via gene conversion favours the preservation of crucial expression motifs via the homogenization of proximal promoter sequences under high selection constraints. However, extensive regulatory subfunctionalization might also have occurred under relative low selection constraints, resulting in functional divergence at the expression level.

Identification of wheat non-specific lipid transfer proteins involved in chilling tolerance

“…Quantitative RT-PCR for abiotic stress and hormone treatments Seeds of T. aestivum were allowed to germinate on filter papers and then moved to containers as previously described by Wang et al (2012). After 36 h, the water was replaced with the Murashige and Skoog (MS) medium (Duchefa Biochemie B.V., Haarlem, Netherlands) in order to grow the plants for 10 days with the photoperiod of 14/10 h and temperature of 28/25°C (day/night) before stress treatments.…”

“…Leaves of 10 or more seedlings from the above treatments were harvested at different time points after treatments, frozen immediately in liquid nitrogen, and stored at -80°C. RNA isolation and quantitative RT-PCR (qRT-PCR) were performed as described previously (Wang et al 2010(Wang et al , 2012. The sequence specificity of each amplified band was cloned and confirmed by sequencing.…”

“…However, the exact function of nsLTPs remains to be clearly established. Several lines of evidence support the function of nsLTPs in cuticle synthesis such as their extracellular localization, the cutin monomer binding capability (Pyee et al 1994;Thoma et al 1994), and the epidermis-specific expression in young aerial growing tissues, where the cuticlar wax usually localizes (Thoma et al 1994;Wang et al 2012). Recent research data demonstrated that the disruption of a nsLTP-like protein (LTPG1) simultaneously altered the cuticular lipid composition and enhanced the susceptibility to the fungal pathogen, Alternaria brasssicola, supporting the overlapping involvement of the nsLTP and cuticle in defense mechanism (Lee et al 2009).…”

“…Recently, plant nsLTPs were extended over nine types using genomic information from Arabidopsis, Oryza sativa and Triticum aestivum, in which type I nsLTPs comprise the maximum number of members belonging to the classical 9 kDa nsLTPs (Boutrot et al 2008). In cereal, a certain number of type I nsLTPs are preserved in genome via the concerted evolution between homeologous chromosomes, however, their functional redundancy or diversification is an open question (Paterson et al 2009;Wang et al 2012).…”

Abundant Type III Lipid Transfer Proteins in Arabidopsis Tapetum Are Secreted to the Locule and Become a Constituent of the Pollen Exine

“…Arabidopsis and rice have 49 and 52 LTP paralogs, respectively, of the nine types. These paralogs have been studied on a global scale with EST databases, microarrays, transcriptome analysis, and LTP-promoter-GFP transgenic analysis (Huang et al, 2009;Edstam et al, 2011;Ng et al, 2012;Wang et al, 2012aWang et al, , 2012b.…”