Abstract
ABSTRACTSome organisms can survive extreme desiccation caused by hypertonic osmotic pressure by entering a state of suspended animation known as osmobiosis. The free-living mycophagous nematode Aphelenchoides besseyi can be induced to enter osmobiosis by soaking in osmolytes. It is assumed that sugars (in particular trehalose) are instrumental for survival under environmental stress. In A. besseyi, two putative trehalose-6-phosphate synthase genes (TPS) encoding enzymes catalyzing trehalose synthesis, and a putative trehalase gene (TRE) encoding enzymes that catalyze hydrolysis of trehalose were identified and then characterized based on their transcriptome. RT-qPCR analyses showed that each of these genes is expressed as mRNA when A. besseyi is entering in, during and recovering from osmobiosis, but only for certain periods. The changes of TRE activity were consistent with the transcript level changes of the TRE gene, and the trehalose level declined at certain periods when the nematodes were in, as well as recovering from, osmobiosis; this suggested that the hydrolysis of threhalose is essential. The feeding method of RNA interference (RNAi) was used to temporarily knock down the expression of each of the TPS and TRE genes. No obviously different phenotype was observed from any of the genes silenced individually or simultaneously, but the survival under hypertonic osmotic pressure reduced significantly and the recovery was delayed. These results indicated that trehalose metabolism genes should play a role in osmobiosis regulation and function within a restricted time frame.
Highlights
Nematodes can turn into a dormant state to survive gradual loss of water (Perry, 1999) when the metabolism is reduced to a level that cannot be detected (Clegg, 2001; Opperman, 2000)
If the water loss is caused by evaporative dehydration it is termed ‘anhydrobiosis’ (Crowe et al, 1992), and when the water loss is caused by hypertonic osmotic pressure the nematodes are in ‘osmobiosis’ (Glazer and Salame, 2000; Yan et al, 2011)
This study focused on the changes of transcript level of trehalose-6phosphate synthase genes (TPS) genes and trehalase gene (TRE) genes as well as TRE activity and trehalose level during osmobiosis
Summary
Nematodes can turn into a dormant state to survive gradual loss of water (Perry, 1999) when the metabolism is reduced to a level that cannot be detected (Clegg, 2001; Opperman, 2000). Received 25 November 2016; Accepted 29 March 2017 nematode, Aphelenchoides besseyi, is widely distributed throughout almost all rice-growing regions. It causes serious nematode diseases in rice and decreases yield by 10-20% in general, and by over 30% in severe cases (Bridge et al, 1990; Wang et al, 1993). A. besseyi is able to last for a long time under hypertonic osmotic pressure, which increases the difficulty of preventing and controlling infestations of these nematodes. A. besseyi can be used as a genetic model to unravel the mechanisms of hypertonic osmotic pressure tolerance within metazoans
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