SignificanceThe plant hormone jasmonate promotes resistance to plant-eating organisms, ranging from pathogenic microbes to mammals. Jasmonate reprograms metabolism to fuel the production of diverse defense compounds and simultaneously inhibits plant growth. Understanding how growth is influenced across a range of defense levels remains unclear, but has important implications for optimizing crop productivity. Using a genetic approach to “tune” the jasmonate response, we assessed the physiological consequences of discrete levels of defense throughout the plant life cycle. Overactivation of jasmonate response led to carbon starvation, near loss of seed production and, under extreme conditions, lethality. Our findings explain the emergence of diverse strategies to keep jasmonate responses at bay and provide new insights into metabolic processes that underlie growth–defense trade-offs.

Strategies to increase rice productivity to meet the global demand have been the main concern of breeders around the world. Although a growing number of functional genes related to crop yield have been characterized, our understanding of its associated regulatory pathways is limited. Using rice as a model, we find that blocking miR396 greatly increases grain yield by modulating development of auxiliary branches and spikelets through direct induction of the growth regulating factor 6 (OsGRF6) gene. The upregulation of OsGRF6 results in the coordinated activation of several immediate downstream biological clades, including auxin (IAA) biosynthesis, auxin response factors, and branch and spikelet development-related transcription factors. This study describes a conserved microRNA (miRNA)-dependent regulatory module that integrates inflorescence development, auxin biosynthesis and signalling pathways, and could potentially be used in engineering high-yield crop plants.

Plant cells contain unique organelles such as chloroplasts with an extensive photosynthetic membrane. In addition, specialized epidermal cells produce an extracellular cuticle composed primarily of lipids, and storage cells accumulate large amounts of storage lipids. As lipid assembly is associated only with discrete membranes or organelles, there is a need for extensive lipid trafficking within plant cells, more so in specialized cells and sometimes also in response to changing environmental condi- Plant cells have many membranes that are generally comparable to those in animal cells including the plasma, mitochondrial, nuclear and peroxisomal membranes. In addition, plant cells contain unique membrane-bound compartments such as the chloroplast, vacuole and symbiosome (1) and have other unique cellular structures composed of lipids, e.g. the cuticle of epidermal cells. As the key photosynthetic organelle in plants, one focus of plant lipid research has been on the chloroplast. It is surrounded by the outer and the inner envelope membranes and encompasses one of the most extensive membrane systems found in nature, the photosynthetic membrane organized into thylakoids. This membrane is unique in its lipid composition with the two galactolipids, monogalactosyldiacylglycerol (MGDG) and digalactosyldiacylglycerol (DGDG), being predominant (2,3). Unlike animal cells that synthesize fatty acids (FAs) in the cytoplasm and assemble glycerolipids primarily in the endoplasmic reticulum (ER), Golgi apparatus and mitochondria (4), plant cells synthesize FAs in the stroma of the chloroplast and assemble glycerolipids mainly by two pathways, the prokaryotic/plastid pathway in the chloroplast envelope membranes and the eukaryotic pathway in the ER (5), aside from lipid assembly or modification in mitochondria and Golgi. It should be noted that while lipid metabolism occurs in plastids other than chloroplasts, for example, chromoplasts in fruits and flowers or leucoplasts in storage tissues, most research on lipid trafficking has focused on chloroplasts. The origin of specific glycerolipids from either the ER or the chloroplast pathways in plants can be determined owing to the specificity of the respective acyltransferases (6,7). The ER-localized acyltransferase preferentially transfers 18 carbon FAs to the sn-2 (carbon 2) position of the glycerol backbone, whereas the chloroplast-localized acyltransferase preferentially transfers 16 carbon FAs to the sn-2 position of the glycerol backbone (6,7). Because of this difference in enzyme specificity, it has been well established that plants use both chloroplast-and ER-derived lipids as precursors in the assembly of chloroplast-specific galactolipids (7-9).www.traffic.dk 915

SignificanceSecond messengers are employed by all organisms to regulate fundamental behaviors, including biofilm formation, motility, metabolism, and pathogenesis in bacteria. We have identified a phospholipase in the El Tor Vibrio cholerae biotype, responsible for the current cholera pandemic, that is directly activated by the second messenger 3′, 3′-cyclic GMP-AMP (cGAMP). Discovery of this proteinaceous bacterial cGAMP effector sheds light on the functions and basic principles of cGAMP signaling. Both this phospholipase and the cGAMP synthase are encoded within the VSP-1 pathogenicity island, unique to the El Tor biotype, and our findings assign a biochemical function to VSP-1 that may contribute to the epidemiological success of El Tor V. cholerae.

Chloroplast membranes with their unique lipid composition are crucial for photosynthesis. Maintenance of the chloroplast membranes requires finely tuned lipid anabolic and catabolic reactions. Despite the presence of a large number of predicted lipid-degrading enzymes in the chloroplasts, their biological functions remain largely unknown. Recently, we described PLASTID LIPASE1 (PLIP1), a plastid phospholipase A that contributes to seed oil biosynthesis. The genome encodes two putative PLIP1 paralogs, which we designated PLIP2 and PLIP3. PLIP2 and PLIP3 are also present in the chloroplasts, but likely with different subplastid locations. In vitro analysis indicated that both are glycerolipid A lipases. In vivo, PLIP2 prefers monogalactosyldiacylglycerol as substrate and PLIP3 phosphatidylglycerol. Overexpression of or severely reduced plant growth and led to accumulation of the bioactive form of jasmonate and related oxylipins. Genetically blocking jasmonate perception restored the growth of the -overexpressing plants. The expression of and , but not, was induced by abscisic acid (ABA), and triple mutants exhibited compromised oxylipin biosynthesis in response to ABA. The triple mutants also showed hypersensitivity to ABA. We propose that PLIP2 and PLIP3 provide a mechanistic link between ABA-mediated abiotic stress responses and oxylipin signaling.