Overexpression of PeAnn1 from Populus euphratica negatively regulates drought resistance in transgenic Arabidopsis thaliana

ObjectiveAnnexins is a large class of annexin families common in prokaryotes and eukaryotes, and participates in many stress response processes such as oxidative stress, heat stress, drought stress and salt stress. However, the role of Populus euphratica annexin family genes in adapting to adverse conditions is still less known. This paper studies the role of P. euphratica Anneixn1 in osmotic stress and drought resistance.

MethodThe mannitol-induced expression of PeAnn1 was examined in P. euphratica leaves. PeAnn1 sequence was compared with annexin genes from P. tomentosa, Arabidopsis thaliana, Glycine soja, and Oryza sative. Phylogenetic tree of annexins was constructed using MEGA 6 software. PeAnn1-overexpressed A. thaliana (PeAnn1-OE1 and PeAnn1-OE2), Annexin1 mutant (atann1) and wild-type A. thaliana (WT) were used in this study. Plants of each genotype were subjected to increasing osmotic stress caused by different concentrations of mannitol (0, 150, 200, 250, 300 mmol/L), drought, and subsequent water recovery. During the period of water stress, the germination rate, root length, chlorophyll content, and fluorescence parameters, H₂O₂, activity of antioxidant enzymes and expression of encoding genes were examined.

ResultThe short-term mannitol treatment up-regulated the expression of PeAnn1 in P. euphratica leaves. The PeAnn1 sequence displayed higher similarity to P. tomentosa Ann1 (PtAnn1) than other plant species. Phylogenetic analysis revealed that the PeAnn1 was highly homologous to the PtAnn1. The survival rate and root growth of A. thaliana plants were inhibited with increasing concentrations of mannitol, and the inhibition was more pronounced in PeAnn1-overexpressing lines as compared to the WT and mutant (P < 0.05). All the measured photosynthesis parameters, such as chlorophyll content, the maximum photon efficiency of PSⅡ (F_v/F_m), the actual photosynthetic quantum yield (ΦPSⅡ), and the relative electron transfer rate (ETR) were lower in the transgenic plants than in the WT and mutant (P < 0.05). After rehydration, the recovery degree of photosynthetic parameters of PeAnn1-transgenic A. thaliana was also lower than the WT. Under osmotic stress, the activities of antioxidant enzymes, such as SOD, POD, and CAT were significantly lower in PeAnn1-overexpressed plants than those of the WT and mutant. In accordance, the expression of these antioxidant enzyme genes showed a same trend as the activities, which could not remove reactive oxygen species, causing oxidative damage.

ConclusionThe above results indicate that overexpression of PeAnn1 decreases the capacity of A. thaliana in the adaptation to water deficit conditions.