Overexpression of BraLTP2, a Lipid Transfer Protein of Brassica napus, Results in Increased Trichome Density and Altered Concentration of Secondary Metabolites.

Nini Tian,Fang Liu,Hongfei Gao,Xinhua Zeng,Pandi Wang,Gang Wu,Xiaohong Yan

doi:10.3390/ijms19061733

Abstract

Plant non-specific lipid transfer proteins (nsLTPs) belong to a large multigene family that possesses complex physiological functions. Trichomes are present on the aerial surfaces of most plants and include both glandular secretory hairs and non-glandular hairs. In this study, BraLTP2 was isolated from Brassica rapa (B. rapa) and its function was characterized in the important oilseed crop Brassica napus (B. napus). B. rapa lipid transfer protein 2 (BraLTP2) belongs to the little-known Y class of nsLTPs and encodes a predicted secretory protein. In ProBraLTP2::GUS (β-glucuronidase) transgenic plants, strong GUS activity was observed in young leaves and roots, while low activity was observed in the anther. It is noteworthy that strong GUS activity was observed in trichomes of the first four leaves of 4-week-old and 8-week-old seedings, however, it disappeared in 12-week-old seedings. In transgenic plants expressing a BraLTP2::GFP (green fluorescent protein) fusion protein, GFP fluorescence localized in the extracellular space of epidermal cells and trichomes. Overexpression of BraLTP2 in B. napus caused an increase in trichome number and altered the accumulation of secondary metabolites in leaves, including 43 upregulated secondary metabolites. Moreover, transgenic plants showed significantly increased activities of antioxidant enzymes. These results suggest that BraLTP2, a new nsLTP gene, may play a role in trichome development and the accumulation of secondary metabolites.

Highlights

Trichomes, which are derived from epidermal cells, are specialized unicellular or multicellular structures that have various functions depending on the plant species and organ [1]
The B. napus (Brassica AC genome) is an allotetraploid species resulting from a cross between B. rapa (A genome) and B. oleracea (C genome), so it is not surprising that the BraLTP2 protein has a high identity to the LTP from B. napus and B. oleracea genomes [48]
The germinated seedlings or rooted transgenic plants were transferred from Murashige & Skoog media into pots containing a mixture of peat moss (PINDSTRUP, Ryomgaard, Danmark) and field soil (3:1), and maintained in a growth chamber at 18 ◦C ± 2 ◦C with a 16 h light and 8 h dark photoperiod, at a light intensity of 44 μmol m−2 s−1 and relative humidity of 60–90%

Summary

Introduction

Trichomes, which are derived from epidermal cells (outermost embryo’s cells), are specialized unicellular or multicellular structures that have various functions depending on the plant species and organ [1]. The criterion that is most often used to classify trichomes is whether they are glandular or not [2]. In the model plant Arabidopsis thaliana (A. thaliana, Cruciferae), only non-glandular trichomes are found, which are unicellular and can be either unbranched, or have two to five branches [3]. Trichomes produce and accumulate secondary metabolites—such as flavonoids [5,6], phenylpropanoids [7], terpenoids [8], alkaloid [9], and defensive proteins [10]—With strong antifungal activity [11]; potential as natural pesticides [12]; and antirdical properties [13,14], such as protection against UV radiation [15,16]. It has been suggested that non-specific lipid transfer proteins (nsLTPs) are involved in the regulation of secondary metabolite biosynthesis, and have a role in resisting biological and abiotic stress [25,26,27]

Methods

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Discussion

Conclusion