Heterologous expression of a plastid EF-Tu reduces protein thermal aggregation and enhances CO2 fixation in wheat (Triticum aestivum) following heat stress

Abstract

Heat stress is a major constraint to wheat production and negatively impacts grain quality, causing tremendous economic losses, and may become a more troublesome factor due to global warming. At the cellular level, heat stress causes denaturation and aggregation of proteins and injury to membranes leading to alterations in metabolic fluxes. Protein aggregation is irreversible, and protection of proteins from thermal aggregation is a strategy a cell uses to tolerate heat stress. Here we report on the development of transgenic wheat (Triticum aestivum) events, expressing a maize gene coding for plastidal protein synthesis elongation factor (EF-Tu), which, compared to non-transgenic plants, display reduced thermal aggregation of leaf proteins, reduced heat injury to photosynthetic membranes (thylakoids), and enhanced rate of CO 2 fixation after exposure to heat stress. The results support the concept that EF-Tu ameliorates negative effects of heat stress by acting as a molecular chaperone. This is the first demonstration of the introduction of a plastidal EF-Tu in plants that leads to protection against heat injury and enhanced photosynthesis after heat stress. This is also the first demonstration that a gene other than HSP gene can be used for improvement of heat tolerance and that the improvement is possible in a species that has a complex genome, hexaploid wheat. The results strongly suggest that heat tolerance of wheat, and possibly other crop plants, can be improved by modulating expression of plastidal EF-Tu and/or by selection of genotypes with increased endogenous levels of this protein.

Analysis of transgenic wheat (Triticum aestivum L.) harboring a maize (Zea mays L.) gene for plastid EF-Tu: segregation pattern, expression and effects of the transgene

“…Previous reports on thermal aggregation of leaf proteins have supported the hypothesis on chaperone activity of chloroplast EF-Tu by showing that increased levels of this protein correlate negatively with protein thermal aggregation Momcilovic and Ristic 2004;Fu et al 2008;Bukovnik et al 2009). However, the previous studies did not clarify whether EF-Tu protects heat-labile proteins from thermal aggregation in a specific or nonspecific manner.…”

“…Transgenic wheat (Triticum aestivum L.) plants that carry maize (Zea mays L.) gene for chloroplast were previously prepared by Fu et al (2008). Zmeftu1 was isolated from a cDNA library that was generated using RNA extracted from the drought and heat-stressed seedlings of maize line B73 (Bhadula et al 2001).…”

“…T 3 generation plants (seedlings) were raised in Petri dishes, and DNA was extracted from the roots and coleoptiles of 7-day-old seedlings (Dellaporta et al 1983). PCR primers and thermal cycling conditions, used to detect Zmeftu1, were similar to those described by Fu et al (2008). A Chi-square test was used to test if the segregation ratio of the transgene (Zmeftu1) fits single gene segregation (SAS 2003).…”

“…Chi-square tests indicated that Zmeftu1 was segregated in a 3:1 ratio (PCR-positive : PCRnegative). PCR primers and thermal cycling conditions, used to detect Zmeftu1 gene insertion in transgenic wheat, were previously described by Fu et al (2008) Plant Mol Biol (2010) 73:339-347 341 transgenic (PCR-positive) plants was assessed both in nonstress and after exposure to a short-term heat stress of 18 h at 45°C. This heat treatment was chosen because our previous study showed that transgenic plants, compared to their non-transgenic counterparts, displayed reduced injury to photosynthetic membranes and enhanced rate of CO 2 fixation following exposure to 45°C for 18 h. Plants of non-transgenic (XC9) and T 2 progeny derived from the T 1 trangenic plant were grown in a growth chamber (day/night temperature of 21/17°C, photoperiod 16/8 h, relative humidity 70-80%, PPF 280 lmol m -2 s -1 ), watered daily, and fertilized weekly using ''Miracle Gro'' fertilizer as outlined above.…”

Hyperconcentrated Sweet Whey, a New Culture Medium That Enhances Propionibacterium freudenreichii Stress Tolerance

“…18) was also induced here. EF-Tu is known to alleviate the negative effect of heat stress by acting as a molecular chaperone (40). It is induced by acid stress in P. freudenreichii (20) and in Lactobacillus delbrueckii (41) and plays a role in osmotic adaptation in Escherichia coli (42).…”