Promoting Production: UPL3 Promoter Variation Modulates Seed Size and Crop Yields

Identifying natural genetic variation, understanding how it influences traits, and utilizing it for crop improvement is a major objective in plant science. Miller et al. (2019) have identified genetic variation in the promoter region of BnaUPL3.C03 from a panel of Brassica napus accessions that can influence seed size, lipid content, and final crop yield

Local manufacturing: A center for photosystem biogenesis

Photosystem biogenesis in the chloroplast requires a concerted effort between synthesis and assembly of components including protein subunits, pigments, and other cofactors that varies both temporally and spatially. Sun et al. (2019) investigate the translation zone (T-zone) of unicellular alga Chlamydomonas reinhardtii (Chlamydomonas) chloroplasts as the primary location for biogenesis of PSI and PSII before redistribution throughout the organelle

Orange is the New Green: Arabidopsis orange represses chloroplast biogenesis

Chloroplast development in germinating seedlings initiates upon illumination. Whereas chloroplasts in true leaves develop directly from proplastids, chloroplasts in cotyledons of dark-grown seedlings develop from an intermediate type of plastid called an etioplas

Evolution of chloroplast retrograde signaling facilitates green plant adaptation to land

Chloroplast retrograde signaling networks are vital for chloroplast biogenesis, operation, and signaling, including excess light and drought stress signaling. To date, retrograde signaling has been considered in the context of land plant adaptation, but not regarding the origin and evolution of signaling cascades linking chloroplast function to stomatal regulation. We show that key elements of the chloroplast retrograde signaling process, the nucleotide phosphatase (SAL1) and 3'-phosphoadenosine-5'-phosphate (PAP) metabolism, evolved in streptophyte algae-the algal ancestors of land plants. We discover an early evolution of SAL1-PAP chloroplast retrograde signaling in stomatal regulation based on conserved gene and protein structure, function, and enzyme activity and transit peptides of SAL1s in species including flowering plants, the fern Ceratopteris richardii, and the moss Physcomitrella patens. Moreover, we demonstrate that PAP regulates stomatal closure via secondary messengers and ion transport in guard cells of these diverse lineages. The origin of stomata facilitated gas exchange in the earliest land plants. Our findings suggest that the conquest of land by plants was enabled by rapid response to drought stress through the deployment of an ancestral SAL1-PAP signaling pathway, intersecting with the core abscisic acid signaling in stomatal guard cells

Evolution of chloroplast retrograde signaling facilitates green plant adaptation to land

Chloroplast retrograde signaling networks are vital for chloroplast biogenesis, operation, and signaling, including excess light and drought stress signaling. To date, retrograde signaling has been considered in the context of land plant adaptation, but not regarding the origin and evolution of signaling cascades linking chloroplast function to stomatal regulation. We show that key elements of the chloroplast retrograde signaling process, the nucleotide phosphatase (SAL1) and 3'-phosphoadenosine-5'-phosphate (PAP) metabolism, evolved in streptophyte algae-the algal ancestors of land plants. We discover an early evolution of SAL1-PAP chloroplast retrograde signaling in stomatal regulation based on conserved gene and protein structure, function, and enzyme activity and transit peptides of SAL1s in species including flowering plants, the fern Ceratopteris richardii, and the moss Physcomitrella patens Moreover, we demonstrate that PAP regulates stomatal closure via secondary messengers and ion transport in guard cells of these diverse lineages. The origin of stomata facilitated gas exchange in the earliest land plants. Our findings suggest that the conquest of land by plants was enabled by rapid response to drought stress through the deployment of an ancestral SAL1-PAP signaling pathway, intersecting with the core abscisic acid signaling in stomatal guard cells

A chloroplast retrograde signal, 3'-phosphoadenosine 5'-phosphate, acts as a secondary messenger in abscisic acid signaling in stomatal closure and germination

Organelle-nuclear retrograde signaling regulates gene expression, but its roles in specialized cells and integration with hormonal signaling remain enigmatic. Here we show that the SAL1-PAP (3′-phosphoadenosine 5′- phosphate) retrograde pathway interacts with abscisic acid (ABA) signaling to regulate stomatal closure and seed germination in Arabidopsis. Genetically or exogenously manipulating PAP bypasses the canonical signaling components ABA Insensitive 1 (ABI1) and Open Stomata 1 (OST1); priming an alternative pathway that restores ABA-responsive gene expression, ROS bursts, ion channel function, stomatal closure and drought tolerance in ost1-2. PAP also inhibits wild type and abi1-1 seed germination by enhancing ABA sensitivity. PAP-XRN signaling interacts with ABA, ROS and Ca2+; up-regulating multiple ABA signaling components, including lowly-expressed Calcium Dependent Protein Kinases (CDPKs) capable of activating the anion channel SLAC1. Thus, PAP exhibits many secondary messenger attributes and exemplifies how retrograde signals can have broader roles in hormone signaling, allowing chloroplasts to fine-tune physiological responsesCE140100008; DE14010114

In Brief - Active Support: GHR1 Is a Pseudokinase That Acts as a Scaffolding Component

Plants balance CO2 uptake with water loss via a complex network of signals regulating stomatal aperture size. Stomata close in response to a number of stimuli, including drought, low light intensity, low air humidity, elevated intercellular CO2 concentration, pathogens, and certain airborne chemicals or pollutants such as ozone. After plants perceive these triggers, multiple signaling cascades involving several kinases and channels ultimately lead to stomatal closure. The plasma membrane receptor kinase GUARD CELL HYDROGEN PEROXIDE RESISTANT1 (GHR1) was previously characterized to mediate abscisic acid- and hydrogen peroxide-regulated stomatal movements, and there is evidence that it functions by phosphorylating SLOW ANION CHANNEL1 (SLAC1; Hua et al., 2012). Sierla et al. (2018) now show that GHR1 is in fact a pseudokinase and present an indepth view of its role in stomatal closure

Choose your own adventure: Mapping out interweaving plant stress response pathways

The sessile nature of a plant has placed an evolutionary pressure on them to develop a highly sophisticated network of signals that encode perception, response and adaptation to a dynamic range of stressors. When a plant experiences drought stress, a number of molecular and physiological processes occur. This includes the production of the retrograde chloroplast-to-nucleus stress signal 3'phosphoadenosine 5'phosphate (PAP), which upregulates the transcription of stress-responsive genes. The initiation of reactive oxygen species (ROS) and stomatal closure signalling pathways occur in parallel. However, the functional role of chloroplasts and specifically PAP-mediated signalling has remained largely enigmatic as to their intersecting role of the two. Thus in my PhD, I tackled these three intertwining pathways that occur in response to stress: retrograde signalling, ROS signalling and stomatal closure signalling. I investigate how PAP affects ROS homeostasis, signalling thresholds, the 'biphasic ROS wave' and the resulting physiological consequences. Here I present evidence how ROS induces signalling cascades, as well as being part of the pathway that propagates signals. As an exemplar proof of concept, I use the guard cell model to show how PAP influences this network of information. Gatekeepers of gas exchange, guard cells mediate stomatal closure as a short-term physiological response that plants utilise to prevent water loss. I show that exogenous application of PAP leads to rapid stomatal closure to a similar extent as the guard cell regulatory hormone abscisic acid (ABA). Significantly, genetic analyses and biochemical manipulation experiments indicate that PAP signalling can supplement the canonical ABA-mediated signalling pathway in guard cells. PAP signalling in stomatal closure includes a dynamic interaction with secondary messengers (including ROS), ion flux induction, and the utilisation of chloroplastic mechanisms separate to ABA signalling. PAP signalling can act at least in part by up-regulating a number of novel calcium protein kinases. My thesis presents evidence of the chloroplast signal PAP having a function role as a molecular signal in response to stress. While we can measure outcomes of drought stress, the complexity of what happens for such responses to occur is an example of how the journey is just as important as the ending