Plant adaptation to low phosphorus availability:Core signaling,crosstalks,and applied implications

Phosphorus(P)is an essential nutrient for plant growth and reproduction.Plants preferentially absorb P as orthophosphate(Pi),an ion that displays low solubility and that is readily fixed in the soil,making P limita-tion a condition common to many soils and Pi fertilization an inefficient practice.To cope with Pi limitation,plants have evolved a series of developmental and physiological responses,collectively known as the Pi starvation rescue system(PSR),aimed to improve Pi acquisition and use efficiency(PUE)and protect from Pi-starvation-induced stress.Intensive research has been carried out during the last 20 years to un-ravel the mechanisms underlying the control of the PSR in plants.Here we review the results of this research effort that have led to the identification and characterization of several core Pi starvation signaling components,including sensors,transcription factors,microRNAs(miRNAs)and miRNA inhibitors,kinases,phosphatases,and components of the proteostasis machinery.We also refer to recent results revealing the existence of intricate signaling interplays between Pi and other nutrients and antagonists,N,Fe,Zn,and As,that have changed the initial single-nutrient-centric view to a more integrated view of nutrient homeostasis.Finally,we discuss advances toward improving PUE and future research priorities.

Roles of Ubiquitination in the Control of Phosphate Starvation Responses in Plants

Throughout evolution, plants have evolved sophisticated adaptive responses that allow them to grow with a limited supply of phos-phate, the preferential form in which the essential macronutrient phosphorus is absorbed by plants. Most of these responses are aimed to increase phosphate availability and acquisition through the roots, to optimize its usage in metabolic processes, and to protect plants from the deleterious effects of phosphate deficiency stress. Regulation of these adaptive responses requires fine percep- tion of the external and internal phosphate levels, and a complex signal transduction pathway that integrates information on the phosphate status at the whole-plant scale. The molecular mecha-nisms that participate in phosphate homeostasis include transcriptional control of gene expression, RNA silencing mediated by microRNAs, regulatory non-coding RNAs of miRNA activity, phosphate transporter trafficking, and post-translational modification of proteins, such as phosphorylation, sumoylation and ubiquitination. Such a varied regulatory repertoire reflects the complexity intrinsic to phosphate surveying and signaling pathways. Here, we describe these regulatory mechanisms, emphasizing the increasing importance of ubiquitination in the control of phosphate starvation responses.

Abscisic Acid Connects Phytohormone Signaling with RNA Metabolic Pathways and Promotes an Antiviral Response that Is Evaded by a Self- Controlled RNA Virus

A complex network of cellular receptors,RNA targeting pathways,and small-molecule signaling provides robust plant immunity and tolerance to viruses.To maximize their fitness,viruses must evolve control mechanisms to balance host immune evasion and plant-damaging effects.The genus Potyvirus comprises plant viruses characterized by RNA genomes that encode large polyproteins led by the P1 protease.A P1 autoinhibitory domain controls polyprotein processing,the release of a downstream functional RNAsilencing suppressor,and viral replication.Here,we show that P1Pro,a plum pox virus clone that lacks the P1 autoinhibitory domain,triggers complex reprogramming of the host transcriptome and high levels of abscisic acid(ABA)accumulation.A meta-analysis highlighted ABA connections with host pathways known to control RNA stability,turnover,maturation,and translation.Transcriptomic changes triggered by P1Pro infection or ABA showed similarities in host RNA abundance and diversity.Genetic and hormone treatment assays showed that ABA promotes plant resistance to potyviral infection.Finally,quantitative mathematical modeling of viral replication in the presence of defense pathways supported self-control of polyprotein processing kinetics as a viral mechanism that attenuates the magnitude of the host antiviral response.Overall,our findings indicate that ABA is an active player in plant antiviral immunity,which is nonetheless evaded by a self-controlled RNA virus.

Propagation of Recombinant Genes through Complex Microbiomes with Synthetic Mini-RP4 Plasmid Vectors

The promiscuous conjugation machinery of the Gram-negative plasmid RP4 has been reassembled in a minimized, highlytransmissible vector for propagating genetically encoded traits through diverse types of naturally occurring microbialcommunities. To this end, the whole of the RP4-encoded transfer determinants (tra, mob genes, and origin of transfer oriT)was excised from their natural context, minimized, and recreated in the form of a streamlined DNA segment borne by anautoselective replicon. The resulting constructs (the pMATING series) could be self-transferred through a variety ofprokaryotic and eukaryotic recipients employing such a rationally designed conjugal delivery device. Insertion of GFP reporterinto pMATING exposed the value of this genetic tool for delivering heterologous genes to both specific mating partners andcomplex consortia (e.g., plant/soil rhizosphere). The results accredited the effective and functional transfer of the recombinantplasmids to a diversity of hosts. Yet the inspection of factors that limit interspecies DNA transfer in such scenarios uncoveredtype VI secretion systems as one of the factual barriers that check otherwise high conjugal frequencies of tested RP4derivatives. We argue that the hereby presented programming of hyperpromiscuous gene transfer can become a phenomenalasset for the propagation of beneficial traits through various scales of the environmental microbiome.