Arabidopsis lipocalins AtCHL and AtTIL have distinct but overlapping functions essential for lipid protection and seed longevity.

Lipocalins are a group of multifunctional proteins, recognized as carriers of small lipophilic molecules, which have been characterized in bacteria and animals. Two true lipocalins have been recently identified in plants, the temperature-induced lipocalin (TIL) and the chloroplastic lipocalin (CHL), the expression of which is induced by various abiotic stresses. Each lipocalin appeared to be specialized in the responses to specific stress conditions in Arabidopsis thaliana, with AtTIL and AtCHL playing a protective role against heat and high light, respectively. The double mutant AtCHL KO × AtTIL KO deficient in both lipocalins was more sensitive to temperature, drought and light stresses than the single mutants, exhibiting intense lipid peroxidation. AtCHL deficiency dramatically enhanced the photosensitivity of mutants (vte1, npq1) affected in lipid protection mechanisms (tocopherols, zeaxanthin), confirming the role of lipocalins in the prevention of lipid peroxidation. Seeds of the AtCHL KO × AtTIL KO double mutant were very sensitive to natural and artificial ageing, and again this phenomenon was associated with the oxidation of polyunsaturated lipids. The presented results show that the Arabidopsis lipocalins AtTIL and AtCHL have overlapping functions in lipid protection which are essential for stress resistance and survival.