Abstract
BackgroundLipocalins are a large and diverse family of small, mostly extracellular proteins implicated in many important functions. This family has been studied in bacteria, invertebrate and vertebrate animals but little is known about these proteins in plants. We recently reported the identification and molecular characterization of the first true lipocalins from plants, including the Apolipoprotein D ortholog AtTIL identified in the plant model Arabidopsis thaliana. This study aimed to determine its physiological role in planta.ResultsOur results demonstrate that the AtTIL lipocalin is involved in modulating tolerance to oxidative stress. AtTIL knock-out plants are very sensitive to sudden drops in temperature and paraquat treatment, and dark-grown plants die shortly after transfer to light. These plants accumulate a high level of hydrogen peroxide and other ROS, which causes an oxidative stress that is associated with a reduction in hypocotyl growth and sensitivity to light. Complementation of the knock-out plants with the AtTIL cDNA restores the normal phenotype. On the other hand, overexpression enhances tolerance to stress caused by freezing, paraquat and light. Moreover, this overexpression delays flowering and maintains leaf greenness. Microarray analyses identified several differentially-regulated genes encoding components of oxidative stress and energy balance.ConclusionThis study provides the first functional evidence that a plant lipocalin is involved in modulating tolerance to oxidative stress. These findings are in agreement with recently published data showing that overexpression of ApoD enhances tolerance to oxidative stress and increases life span in mice and Drosophila. Together, the three papers strongly support a similar function of lipocalins in these evolutionary-distant species.
Highlights
Lipocalins are a large and diverse family of small, mostly extracellular proteins implicated in many important functions
Overexpression of the AtTIL cDNA resulted in a 4fold accumulation of the protein compared to the WT (Fig. 1b, OEX)
The downregulation of AtTIL expression (KO) has no visible effect on plant growth and development compared to the WT (Fig. 1c)
Summary
Lipocalins are a large and diverse family of small, mostly extracellular proteins implicated in many important functions. This family has been studied in bacteria, invertebrate and vertebrate animals but little is known about these proteins in plants. Lipocalins are small ligand-binding proteins found in bacteria and in invertebrate and vertebrate animals. Over 40 lipocalin members have been identified from all kingdoms [1] They show a simple tertiary structure which gives them the ability to bind small, generally hydrophobic, molecules. It was recently shown that the insect glial Lazarillo lipocalin (GLaz) possesses a protective role against oxidative stress conditions and that its absence increases lipid peroxydation, reduces life span and accelerates neurodegeneration in Drosophila [2]. Its overexpression protects against the effects of starvation, hypoxia and hyperoxia, and extends the fly's life span [3]
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