The toc132toc120 heterozygote mutant of Arabidopsis thaliana accumulates reduced levels of hexadecatrienoic acid

Split-Ubiquitin Two-Hybrid Screen for Proteins Interacting with slToc159-1 and slToc159-2, Two Chloroplast Preprotein Import Receptors in Tomato (Solanum lycopersicum)

The post-translational import of nuclear-encoded chloroplast preproteins is critical for chloroplast biogenesis, and the Toc159 family of proteins is the receptor for this process. Our previous work identified and analyzed the Toc GTPase in tomato; however, the tomato-specific transport substrate for Toc159 is still unknown, which limits the study of the function of the TOC receptor in tomato. In this study, we expand the number of preprotein substrates of slToc159 receptor family members using slToc159-1 and slToc159-2 as bait via a split-ubiquitin yeast two-hybrid membrane system. Forty-one specific substrates were identified in tomato for the first time. Using slToc159-1GM and slToc159-2GM as bait, we compared the affinity of the two bait proteins, with and without the A domain, to the precursor protein, which suggested that the A domain endowed the proproteins with subclass specificity. The presence of the A domain enhanced the interaction intensity of slToc159-1 with the photosynthetic preprotein but decreased the interaction intensity of slToc159-2 with the photosynthetic preprotein. Similarly, the presence of the A domain also altered the affinity of slToc159 to non-photosynthetic preproteins. Bimolecular fluorescence complementation (BiFC) analysis showed that A domain had the ability to recognize the preprotein, and the interaction occurred in the chloroplast. Further, the localization of the A domain in Arabidopsis protoplasts showed that the A domain did not contain chloroplast membrane targeting signals. Our data demonstrate the importance of a highly non-conserved A domain, which endows the slToc159 receptor with specificity for different protein types. However, the domain containing the information on targeting the chloroplast needs further study.

Fatty acid desaturases (FADs) modulate multiple lipid metabolism pathways to improve plant resistance

BACKGROUND

Biological and abiotic stresses such as salt, extreme temperatures, and pests and diseases place major constraints on plant growth and crop yields. Fatty acids (FAs) and FA- derivatives are unique biologically active substance that show a wide range of functions in biological systems. They are not only participated in the regulation of energy storage substances and cell membrane plasm composition, but also extensively participate in the regulation of plant basic immunity, effector induced resistance and systemic resistance and other defense pathways, thereby improving plant resistance to adversity stress. Fatty acid desaturases (FADs) is involved in the desaturation of fatty acids, where desaturated fatty acids can be used as substrates for FA-derivatives.

OBJECTIVE

In this paper, the role of omega-FADs (ω-3 FADs and ω-6 FADs) in the prokaryotic and eukaryotic pathways of fatty acid biosynthesis in plant defense against stress (biological and abiotic stress) and the latest research progress were summarized. Moreover' the existing problems in related research and future research directions were also discussed.

RESULTS

Fatty acid desaturases are involved in various responses of plants during biotic and abiotic stress. For example, it is involved in regulating the stability and fluidity of cell membranes, reactive oxygen species signaling pathways, etc. In this review, we have collected several experimental studies to represent the differential effects of fatty acid desaturases on biotic and abiotic species.

CONCLUSION

Fatty acid desaturases play an important role in regulating biotic and abiotic stresses.

The toc132toc120 heterozygote mutant of Arabidopsis thaliana accumulates decreased levels of the major chloroplast lipids

We used ESI-MS/MS to profile glycerolipids in a mutant of Arabidopsis thaliana that is null and heterozygous for the TOC132 and TOC120 genes, and is referred to as the toc132toc120± mutant. The goal was to assess the impact of a defective atToc132/120 receptor on the accumulation of chloroplast lipids. The mutant accumulated decreased amounts of monogalactosyldiacylglycerol (MGDG), digalactosyldiacylglycerol (DGDG) and phosphatidylglycerol (PG). In the cold-acclimated mutant, PG accumulated at the control levels. However, 34:4-PG (18:3/16:1Δ^3trans) was significantly decreased, which indicates that the mutant was impaired in synthesis of the chloroplast-derived PG. Major molecular species of MGDG and DGDG were significantly decreased, which was indicative of the decreased levels of triunsaturated fatty acids in galactolipids. The cold-acclimated mutant accumulated increased levels of phosphatidylcholine (PC), phosphatidylethanolamine (PE) and phosphatidylserine (PS), which indicate that defect in the atToc132/120 receptor did not impair the ER pathway of lipid synthesis. Both cold-acclimated wildtype and mutant plants accumulated increased levels of phosphatidic acid (PA). The increased levels of major molecular species of PA suggest that some pool of PA was derived from degradation of both the chloroplast and extra-chloroplast lipids. The cold-acclimated mutant had decreased double bond index (DBI) and increased acyl chain length (ACL), which was indicative of decreased membrane fluidity. However, a decrease in the ratio of MGDG to DGDG indicate that the mutant was capable of remodeling membrane lipids in response to low temperatures. We conclude that the defective Toc132/120 receptor resulted in decreased synthesis of chloroplast lipids and decreased membrane fluidity.

Ozone-induced lipid changes in the wildtype and toc132toc120 heterozygote mutant of Arabidopsis thaliana

We measured the fatty acids and lipid content in the wildtype and toc132toc120 heterozygote mutant of Arabidopsis thaliana that were exposed to elevated levels of ozone. The goal was to assess whether a defective atToc132/120 receptor would alter the mutant's response to ozone-induced stress. Increased malondialdehyde (MDA) levels were measured in wildtype plants that were exposed to ozone for 3 h and left in an ozone-free environment for 21 h. The increased levels of MDA were not positively correlated with changes in the levels of triunsaturated fatty acids from which MDA is derived. In both the wildtype and mutant plants, absolute amounts of the glycerolipids were not altered by ozone treatment. The untreated mutant, however, accumulated decreased levels of chloroplast lipids and triunsaturated fatty acids. In ozone-treated wildtype, the levels of 16:3 were significantly decreased and this was mirrored by decreased levels of TOC132 and FAD5 transcripts, and increased levels of SP1 E3 ligase transcripts. These data suggest a possible increase in protein ubiquitination under ozone-induced stress. In contrast, in ozone-treated mutant, the FAD5 transcripts accumulated at the control level. The untreated mutant, however, accumulated significantly increased levels of CAT1 and FAD7 transcripts, which indicates that a defective chloroplast receptor induced cellular stress. In ozone-treated wildtype, there was a small increase in 34:6-phosphatidic acid, which indicates that a small amount of the chloroplast-derived MGDG was degraded in response to ozone-induced stress. Overall, these data indicate that the wildtype and mutant responded differently in lipid composition and oxidation to ozone-induced stress.