The first step in photosynthesis is the light-driven reduction (splitting) of water to provide the electrons for the photosynthetic electron transport chains as well as protons for the establishment of a proton gradient. The water-splitting reaction occurs on the lumenal side of the thylakoid membrane and is driven by the light energy captured by the photosystems. It is interesting to note that this oxidation of water conveniently produces the waste product O 2 that is vital for cellular respiration . The molecular oxygen formed by the reaction is released into the atmosphere.
My lab also studies the function and regulation of RNAi pathway components, mostly Argonaute (AGO) proteins in plant immunity. AGO proteins are the core components of RNAi complexes, which selectively bind with small RNAs and silence target genes with complementary sequences. We discovered that Arabidopsis AGO2 positively regulates antibacterial immunity by associating with miR393*, which targets a Golgi-localized SNARE gene MEMB12 and leads to increased secretion of antimicrobial peptide and confers resistance. Since miR393 also contributes to antibacterial immunity by suppressing auxin receptors, miR393*/miR393 represent a novel example of a miRNA*/miRNA pair that functions in the same cellular pathway (host immunity) through two distinct AGOs. We further demonstrated that small RNA duplex structures and AGO PIWI domain contribute to the selective loading of small RNAs in different AGO proteins, AGO1 and AGO2. We currently focus on the regulation and modification of AGO proteins in responses to pathogen attacks.
Japanese plums represent the most abundant and variable group among tree species and include most of the fresh-market plums commercialized worldwide. We characterized and compared two Japanese plum cultivars, “Santa Rosa” (SR) and its bud-sport mutant “Sweet Miriam” (SM). These cultivars share the same genetic background but display contrasting ripening behaviors (SR, climacteric and SM, non-climacteric). Both cultivars differ in their sugar metabolism conferring the SM fruits with unusual quality properties (lower glucose and fructose, higher sorbitol and galactose-metabolism related sugars, etc). The main objective of this research is to characterize the differences in the complex sugar metabolic pathways between the cultivars and their possible crosstalk with ethylene biosynthesis-related enzymes, underlying their climacteric and non-climacteric fruit ripening behaviors. Fruits from each each cultivar were harvested at an early (S2: pit hardening) and late (S4: fully-ripe) stages of fruit development and assessed using a Systems Biology approach. Transcriptomics, proteomics and metabolomics methodologies, together with targeted gene expression and enzymatic activity assays were analyzed to reveal complex sugar metabolic interrelations and identify differences between the cultivars that could be associated to the observed changes in sugar homeostasis as well as ethylene biosynthesis and ethylene signaling. This experimental system provides a unique tool to study metabolic pathways underlying climacteric and non-climacteric fruit ripening behaviors and offers several practical applications. Understanding mechanisms that allow fruits to ‘switch’ to a sorbitol-based metabolism would have a great industry impact, since sorbitol is an alternative and healthier natural sweetener to sucrose. In addition, it could also allow the identification of candidate genes for breeding programs focused on fruit quality improvement.