Abstract
The sunflower (Helianthus annuus L.) is among the most widely cultivated crops in the world due to the oilseed production. Lipid transfer proteins (LTPs) are low molecular mass proteins encoded by a broad multigenic family in higher plants, showing a vast range of functions; these proteins have not been characterised in sunflower at the genomic level. In this work, we exploited the reliable genome sequence of sunflower to identify and characterise the LTP multigenic family in H. annuus. Overall, 101 sunflower putative LTP genes were identified using a homology search and the HMM algorithm. The selected sequences were characterised through phylogenetic analysis, exon–intron organisation, and protein structural motifs. Sunflower LTPs were subdivided into four clades, reflecting their genomic and structural organisation. This gene family was further investigated by analysing the possible duplication origin of genes, which showed the prevalence of tandem and whole genome duplication events, a result that is in line with polyploidisation events that occurred during sunflower genome evolution. Furthermore, LTP gene expression was evaluated on cDNA libraries constructed on six sunflower tissues (leaf, root, ligule, seed, stamen, and pistil) and from roots treated with stimuli mimicking biotic and abiotic stress. Genes encoding LTPs belonging to three out of four clades responded specifically to external stimuli, especially to abscisic acid, auxin, and the saline environment. Interestingly, genes encoding proteins belonging to one clade were expressed exclusively in sunflower seeds. This work is a first attempt of genome-wide identification and characterisation of the LTP multigenic family in a plant species.
Highlights
Sunflower (Helianthus annuus L.) is an annual plant belonging to the Asteraceae, the largest family of the Angiosperm clades
Pofrofitveienmseoqtiufsenincethceomprpoatreii-n ssoenqsuaelnlocwese(dFuigsutroes1u)b. divide the family into 4 groups, based on the presence of five motifs in theLpirpoidteitnrasnesqfeurenpcroeste(iFnigseuqreue1n).ces in the sunflower genome that mainly correspond to GrouLpip1idctoruanldsfbeer parsosoteciinatseedquweinthcensoinn-sthpeecsifiucnLflToPwserofgteynpoemse1tahnadt m2a[i9n]l,ycoconrsriedseproinngdtthoe Graronugpe 1ofcmouolldecbuelaarsswoeciiagthetdswhoitwhnnobny-stpheicsifgicroLuTpPs(Foigf utyrpee2s),1wahnedre2a[s9]H, McoMnsEidRer[i2n6g] wthaes raabnlgeetoofremtroileevceultahrewmeoigsthtdisvheorwgennbt ymtehmisbgerrsouopf t(hFeigLuTrPe 2m),uwltihgeerneiacsfHamMilMy EinRH[2. 6a]nwnuauss a(bGlerotuoprse2tr,i3e,v4e, tahnedmpoarsttiadlilvyeGrgreonutpm1)e.mbers of the Lipid transfer proteins (LTPs) multigenic family in H. annuus (GrouAps 2fo, r3,g4e,naonmdipc alortcialilsyaGtioronu, pu1t)a. tive H. annuus LTPs (HaLTPs) genes were widespread on all the sunflower chromosomes, at different frequencies
HaLTP gene copies were grouped in chromosome regions (Figure 3)
Summary
Sunflower (Helianthus annuus L.) is an annual plant belonging to the Asteraceae, the largest family of the Angiosperm clades. It is an important source of vegetable oil and is extensively cultivated worldwide. As in other plant species, lipids play important roles in growth and development, building and maintaining energy stores and membranes necessary for the compartmentalisation of different metabolic pathways in the cell [5]. Lipids mediate responses to stress by being involved in cell signalling, constructing the surface cuticle layer, and protecting cells from water stress-related desiccation. Membrane lipids mediate cell signalling associated with responses to the environment [5]
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