What We’re Reading: Dec 16

Previewing Pollen Biology special issue of Plant Physiology

pollenspecialissuseIn Plant Physiology Preview you can get a head start on reading the excellent set of articles from a forthcoming special issue on Pollen Biology. Updates and research articles cover all aspects of this crucial part of reproductive biology, from the complex cell biology that underpins polar growth of pollen tubes to the signals exchanged between pistil and pollen that control mate selection. Selected reveiws cover Gametophytic pollen tube guidance (10.1104/pp.16.01571), Pollen-pistil interactions and their role in mate selection (10.1104/pp.16.01286), and Signaling with ions: the keystone for apical cell growth and morphogenesis in pollen tubes (10.1104/pp.16.01561). Plant Physiol. http://www.plantphysiol.org/content/early/recent Tags: Botany, Cell Biology, Development, Growth Regulation, Signals and Responses

Metabolic control of tobacco pollination by sugars and invertases ($)

sucrosepollenA germinated pollen grain extends a pollen tube through the stigma and style of the flower to deliver two sperm cells to an ovule.  Tip-directed growth of the pollen tube requires a large energy input, but how does the pollen tube obtain energy while growing through the flower tissues?  Goetz et al. investigated the roles of extracellular cell wall invertase (cwINV) enzymes in supplying energy to the growing pollen tube in N. tabacum.  cwINVs break down sucrose into hexose sugars that can be transported into the pollen tube.  In tobacco pollen, NtcwINV2 is postulated to regulate NtcwINV1 for control of sucrose breakdown, and RNA transcript levels for both NtcwINV1 and NtcwINV2 peaked in pollinated pistils.  The authors found separate pollen tube import pathways for sucrose and hexose sugars formed by cwINV cleavage of sucrose, which are supported by in vitro pollen germination assays indicating glucose stimulates pollen germination while sucrose stimulates pollen tube extension.  To show how hexoses can be imported into the pollen tube, the authors characterize two hexose transporters, NtMST2 and NtMST3.  With in situ hybridization, NtMST2 and NtMST3 were detected in growing pollen tubes, and their expression patterns overlap with NtcwINV2.  The authors present a model for NtcwINV enzymes and NtMST transporters cooperatively regulating the availability of sugars for pollen germination and tube growth. (Summary by Daniel Czerny) Plant Physiol. Tags: Biochemistry, Bioenergy, Cell Biology, Growth Regulation, Metabolism

Review: Volvox as a model for embryogenesis, morphogenesis and differentiation

volvoxMatt and Umen introduce the multicellular green alga Volvox carteri as a model for developmental studies. They provide an overview of embryonic patterning including the role of asymmetric cell divisions, inversion, (a process with some similarities to vertebrate gastrulation), and the role of cell size in cell fate. They conclude with a summary of genetic and other tools for the study of Volvox biology, as well as a list of open questions. This would be a very nice paper for students studying development, as Volvox is a less familiar but nonetheless interesting model species. Devel. Biol. 10.1016/j.ydbio.2016.07.014 Tags: Botany, Cell Biology, Development, Education and Outreach, Evolution,

Review: Competence to flower

competencetoflowerThe transition between vegetative and reproductive stages in the plant life cycle implies a change in the developmental program of the shoot apical meristem to stop developing leaves and start developing floral buds. The factors that allow this transition to happen are many and the underlying mechanisms by which those factors induce flowering have been extensively studied. In this review, Hyun et al. go into the details of how miRNAs, especially miR156 and miR172, control when the plants get the competence to flower, and discuss their regulation of the SPL transcription factors and association with gibberellins. This miR156/SPL system seems to be ancient and quite conserved in flowering plants. (Summary by Gaby Auge) Plant Physiol. doi:10.1104/pp.16.01523 Tags: Development, Gene Regulation, Genetics, Growth Regulation

Review: The Plant Microbiota: Systems-Level Insights and Perspectives ($)

microbiotaTerrestrial plants are hosts to diverse types of microbes, predominantly bacteria, that affect plant health and growth in numerous ways. The major types of plant microbiota include plant pathogens, arbuscular mycorrhizal (AM) fungi, endophytes (residing within plant tissues), epiphytes (residing on plant surfaces), etc. Müller et al. review various aspects of plant microbiota research. Phylogenetic research suggests that in spite of some differences, the microbial communities on above- and belowground organs typically exhibit a defined taxonomic structure composed of mainly Proteobacteria, Actinobacteria, Bacteroidetes, and Firmicutes. A holistic understanding of entire plant microbiomes can be gained by an integration of various omics data. Insights into how host genotype affects bacterial community establishment come from Synthetic Communities (SynComs), involving gnotobiotic systems in which a plant grown under microbe-free conditions can be experimentally inoculated. A better understanding of the various plant host-microbe interactions taking place at a systems level could help with microbiome applications such as improved plant health and phytoremediation. (Summary by Bhavisha Sheth) Annu. Rev. Genet. 10.1146/annurev-genet-120215-034952 Tags: Biotic Interactions, Ecophysiology, Environmental Plant Biology, Genomics

A dephytylase involved in chlorophyll turnover

chlorophyllaseChlorophyll has an aliphatic phytol side chain that anchors it to light-harvesting complexes. During senescence, chlorophyll is degraded first by the enzymatic removal of Mg to produce pheophytin, which is dephytlated by pheophytinase. Through the identification of a mutant allele with elevated enzymatic activity, Lin et al. have now identified an enzyme, CLD1, that directly dephytylates chlorophyll. The authors propose that CLD1 is involved in the steady-state turnover of chlorophyll in green tissues, and is required for thermotolerance to moderately high temperatures. Plant Cell 10.1105/tpc.16.00478 Tags: Abiotic interactions, Biochemistry, Bioenergetics, Metabolism, Physiology

Genetic basis of primrose floral dimorphism

primulaSelf-fertilization in Primula is avoided by the production of two flower forms (morphs), one with a long style in which the stigma is elevated above the anthers (the L morph or pin) and one with a short style in which the anthers are well above the stigma (the S morph or thrum), although there are also populations in which the anther and stigma are of the same height (either as long homostyle or short homostyle). The S locus is a complex genetic locus known to specify the different flower forms. Li et al. showed that thrums (S/s) carry a form of the S locus that has more genes than the form found in pins (s/s). One of the thrum-specific genes CYP encodes a cytochrome P450 enzyme shown recently by Huu et al to break down brassinosteroid hormones, thus accounting for the shorter styles in the thrums. Li et al. also show that homostyles arise from alterations in the S locus, specifically in the CYP or GLO genes.  eLIFE 10.7554/eLife.17956 and Nature Plants 10.1038/nplants.2016.188 Tags: Botany, Development, Evolution, Genetics

Learning by association in plants

learningAnimals can easily establish associations between environmental cues and food sources, acquiring conditional information that guides their foraging behaviour and in consequence, their survival. Proving whether plants show association or conditional learning has been tricky, but fortunately for us, Gagliano et al. have come with a way to show that learning by association is, in fact, more ubiquitous than thought in the tree of life. With a couple of extremely simple but clever experiments, the authors unequivocally show that pea seedlings previously trained with a conditional stimulus can predict a future source of light, prevailing over innate phototropism responses. This conditioned response is mostly evident when the training overlaps the subjective day, suggesting that this behavior is regulated by metabolic demands. And people say plants are boring… I don’t think so! (Summary by Gaby Auge) Scientific Reports, doi:10.1038/srep38427 Tags: Botany, Evolution, Growth Regulation, Signals and Responses

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