Over the past few years, three photorespiratory bypasses have been introduced into plants, two of which led to observable increases in photosynthesis and biomass yield. However, most of the experiments were carried out using Arabidopsis under controlled environmental conditions, and the increases were only observed under low-light and short-day conditions. In this study, we designed a new photorespiratory bypass (called GOC bypass), characterized by no reducing equivalents being produced during a complete oxidation of glycolate into CO 2 catalyzed by three rice-self-originating enzymes, i.e., glycolate oxidase, oxalate oxidase, and catalase. We successfully established this bypass in rice chloroplasts using a multi-gene assembly and transformation system. Transgenic rice plants carrying GOC bypass (GOC plants) showed significant increases in photosynthesis efficiency, biomass yield, and nitrogen content, as well as several other CO 2 -enriched phenotypes under both greenhouse and field conditions. Grain yield of GOC plants varied depending on seeding season and was increased significantly in the spring. We further demonstrated that GOC plants had significant advantages under high-light conditions and that the improvements in GOC plants resulted primarily from a photosynthetic CO 2 -concentrating effect rather than from improved energy balance. Taken together, our results reveal that engineering a newly designed chloroplastic photorespiratory bypass could increase photosynthetic efficiency and yield of rice plants grown in field conditions, particularly under high light.
BackgroundGrapes are a major fruit crop around the world. Heat stress can significantly reduce grape yield and quality. Changes at the molecular level in response to heat stress and subsequent recovery are poorly understood. To elucidate the effect of heat stress and subsequent recovery on expression of genes by grape leaves representing the classic heat stress response and thermotolerance mechanisms, transcript abundance of grape (Vitis vinifera L.) leaves was quantified using the Affymetrix Grape Genome oligonucleotide microarray (15,700 transcripts), followed by quantitative Real-Time PCR validation for some transcript profiles.ResultsWe found that about 8% of the total probe sets were responsive to heat stress and/or to subsequent recovery in grape leaves. The heat stress and recovery responses were characterized by different transcriptional changes. The number of heat stress-regulated genes was almost twice the number of recovery-regulated genes. The responsive genes identified in this study belong to a large number of important traits and biological pathways, including cell rescue (i.e., antioxidant enzymes), protein fate (i.e., HSPs), primary and secondary metabolism, transcription factors, signal transduction, and development. We have identified some common genes and heat shock factors (HSFs) that were modulated differentially by heat stress and recovery. Most HSP genes were upregulated by heat stress but were downregulated by the recovery. On the other hand, some specific HSP genes or HSFs were uniquely responsive to heat stress or recovery.ConclusionThe effect of heat stress and recovery on grape appears to be associated with multiple processes and mechanisms including stress-related genes, transcription factors, and metabolism. Heat stress and recovery elicited common up- or downregulated genes as well as unique sets of responsive genes. Moreover, some genes were regulated in opposite directions by heat stress and recovery. The results indicated HSPs, especially small HSPs, antioxidant enzymes (i.e., ascorbate peroxidase), and galactinol synthase may be important to thermotolerance of grape. HSF30 may be a key regulator for heat stress and recovery, while HSF7 and HSF1 may only be specific to recovery. The identification of heat stress or recovery responsive genes in this study provides novel insights into the molecular basis for heat tolerance in grape leaves.
In several eukaryotic organisms, heterochromatin (HC) in the introns of genes can regulate RNA processing, including polyadenylation, but the mechanism underlying this regulation is poorly understood. By promoting distal polyadenylation, the bromo-adjacent homology (BAH) domain-containing and RNA recognition motif-containing protein ASI1 and the H3K9me2-binding protein EDM2 are required for the expression of functional full-length transcripts of intronic HC-containing genes in Here we report that ASI1 and EDM2 form a protein complex in vivo via a bridge protein, ASI1-Immunoprecipitated Protein 1 (AIPP1), which is another RNA recognition motif-containing protein. The complex also may contain the Pol II CTD phosphatase CPL2, the plant homeodomain-containing protein AIPP2, and another BAH domain protein, AIPP3. As is the case with dysfunction of ASI1 and EDM2, dysfunction of AIPP1 impedes the use of distal polyadenylation sites at tested intronic HC-containing genes, such as the histone demethylase gene, resulting in a lack of functional full-length transcripts. A mutation in causes silencing of the transgene and genome-wide CHG hypermethylation at gene body regions, consistent with the lack of full-length functional transcripts in the mutant. Interestingly, compared with, , and mutations, mutations in ,, and cause the opposite effects on the expression of intronic HC-containing genes and other genes, suggesting that CPL2, AIPP2, and AIPP3 may form a distinct subcomplex. These results advance our understanding of the interplay between heterochromatic epigenetic modifications and RNA processing in higher eukaryotes.
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