Abstract
Lipid transfer proteins (LTPs), a class of small, ubiquitous proteins, play critical roles in various environmental stresses. However, their precise biological functions remain unknown. Here we isolated an extracellular matrix-localised LTP, NtLTP4, from Nicotiana tabacum. The overexpression of NtLTP4 in N. tabacum enhanced resistance to salt and drought stresses. Upon exposure to high salinity, NtLTP4-overexpressing lines (OE lines) accumulated low Na+ levels. Salt-responsive genes, including Na+/H+ exchangers (NHX1) and high-affinity K+ transporter1 (HKT1), were dramatically higher in OE lines than in wild-type lines. NtLTP4 might regulate transcription levels of NHX1 and HKT1 to alleviate the toxicity of Na+. Interestingly, OE lines enhanced the tolerance of N. tabacum to drought stress by reducing the transpiration rate. Moreover, NtLTP4 could increase reactive oxygen species (ROS)-scavenging enzyme activity and expression levels to scavenge excess ROS under drought and high salinity conditions. We used a two-hybrid yeast system and screened seven putative proteins that interact with NtLTP4 in tobacco. An MAPK member, wound-induced protein kinase, was confirmed to interact with NtLTP4 via co-immunoprecipitation and a firefly luciferase complementation imaging assay. Taken together, this is the first functional analysis of NtLTP4, and proves that NtLTP4 positively regulates salt and drought stresses in N. tabacum.
Highlights
Plants frequently encounter environmental stresses, such as salinity, drought, heavy metal, low temperature and microbial infections[1,2]
The analysis of the Na+ content further clarified the role of NtLTP4 by partially regulating the transcription levels of NHX1 and high-affinity K+ transporter1 (HKT1) to alleviate the toxicity of Na+
Lipid transfer proteins (LTPs) are abundant, small and lipid-binding proteins that are involved in various physiological processes in plants, including cutin synthesis, somatic embryogenesis, post-meiotic anther development, pathogen defence and long-distance signalling of systemic acquired resistance (SAR)[16,18,19,20,34,35]
Summary
Plants frequently encounter environmental stresses, such as salinity, drought, heavy metal, low temperature and microbial infections[1,2]. All examples of LTPs contain eight cysteine residues (C...C...CC...CXC...C...C) that form four conserved disulfide bridges that stabilise a bundle of four alpha-helices[13] This bundle forms a hydrophobic pocket with a unique plasticity to accommodate a fatty acid, phospholipids or acyl-CoA14,15. The first family of LTPs, named type I-LTP, possesses molecular masses of approximately 10 kDa and contains a signal peptide that is generally between 21–27 amino acids at the N-terminus[16]. That possess molecular masses of approximately 7 kDa and contains a signal peptide between 27–35 amino acids[17] The importance of these small proteins in plant growth and development has become increasingly clear, such as in cutin synthesis[16], post-meiotic anther development[18], and pathogen defence[19,20]. Illuminating the specific functions of other LTPs in tobacco is important
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