Misexpression of a chloroplast aspartyl protease leads to severe growth defects and alters carbohydrate metabolism in Arabidopsis

The crucial role of carbohydrate in plant growth and morphogenesis is widely recognized. In this study, we describe the characterization of nana, a dwarf Arabidopsis (Arabidopsis thaliana) mutant impaired in carbohydrate metabolism. We show that the nana dwarf phenotype was accompanied by altered leaf morphology and a delayed flowering time. Our genetic and molecular data indicate that the mutation in nana is due to a transfer DNA insertion in the promoter region of a gene encoding a chloroplast-located aspartyl protease that alters its pattern of expression. Overexpression of the gene (oxNANA) phenocopies the mutation. Both nana and oxNANA display alterations in carbohydrate content, and the extent of these changes varies depending on growth light intensity. In particular, in low light, soluble sugar levels are lower and do not show the daily fluctuations observed in wild-type plants. Moreover, nana and oxNANA are defective in the expression of some genes implicated in sugar metabolism and photosynthetic light harvesting. Interestingly, some chloroplast-encoded genes as well as genes whose products seem to be involved in retrograde signaling appear to be down-regulated. These findings suggest that the NANA aspartic protease has an important regulatory function in chloroplasts that not only influences photosynthetic carbon metabolism but also plastid and nuclear gene expression

Caratterizzazione fisiologica e molecolare di un mutante nano di Arabidopsis thaliana

Un mutante nano di A. thaliana (L.) Heynh è stato isolato, nel corso di uno screening su turanosio tra linee mutate T-DNA tagged, in quanto ipersensibile a questo analogo non metabolizzabile del saccarosio. Le principali caratteristiche fenotipiche del mutante nana sono le ridotte dimensioni, un marcato ritardo nella fioritura e le foglie di color verde scuro. Osservazioni al CRIO-SEM hanno indicato come le cellule della lamina fogliare di nana siano più piccole di quelle del wild-type Columbia gl1. Sono stati identificati due siti di inserzione del T-DNA, mediante la tecnica della TAIL-PCR: (1) sul promotore del gene At3g12700, che codifica per una aspartyl proteasi, ed è simile a una CND41, DNA binding protein chloroplast nucleoids in T. nicotiana; (2) sull’ultimo introne del gene At1g73720, fattore trascrizionale in D. melanogaster, denominato Will Die Slowly. L’attenzione è stata concentrata su At3g12700, poiché in tabacco è stato identificato un mutante knock-out per un gene simile al CND41, con le stesse caratteristiche fenotipiche; il relativo sito di inserzione è stato completamente sequenziato e la sua espressione analizzata mediante Real-Time PCR. In un primo momento sembrava che nana over-esprimesse At3g12700, ma un’analisi più accurata ha rilevato una possibile modulazione del gene da parte dell’intensità luminosa e una variazione nel livello di espressione, in funzione del ciclo circadiano. È risultato interessante come l’espressione di At3g12700 sia indotto dalla presenza nel mezzo agarizzato di saccarosio 90mM, suggerendo una possibile interazione tra lo sugar sensing e la biosintesi delle gibberelline. Inoltre, le dimensioni e la forma delle foglie sono state ristabilite a quelle di gl1 con l’applicazione di gibberelline in una soluzione di metanolo, direttamente sull’apice meristematico, indicando che una riduzione nel contenuto di GAs è la causa principale del fenomeno di nanismo. Per questo motivo, sono state quantificate le GAs endogene del mutante, rispetto a quelle del wild-type, mediante GC-MS. Sono state così individuate delle variazioni nel contenuto delle GAs in nana

Impact of an arbuscular mycorrhizal fungus versus a mixed microbial inoculum on the transcriptome reprogramming of grapevine roots

Grapevine, cultivated for both fruit and beverage production, represents one of the most economically important fruit crops worldwide. With the aim of better understanding how grape roots respond to beneficial microbes, a transcriptome sequencing experiment has been performed to evaluate the impact of a single arbuscular mycorrhizal (AM) fungal species (Funneliformis mosseae) versus a mixed inoculum containing a bacterial and fungal consortium, including different AM species, on Richter 110 rootstock. Results showed that the impact of a single AM fungus and of a complex microbial inoculum on the grapevine transcriptome differed. After 3 months, roots exclusively were colonized after the F. mosseae treatment and several AM marker genes were found to be upregulated. The mixed inoculum led only to traces of colonization by AM fungi, but elicited an important transcriptional regulation. Additionally, the expression of genes belonging to categories such as nutrient transport, transcription factors, and cell wall-related genes was significantly altered in both treatments, but the exact genes affected differed in the two conditions. These findings advance our understanding about the impact of soil beneficial microbes on the root system of a woody plant, also offering the basis for novel approaches in grapevine cultivation

Physiological responses to Megafol® treatments in tomato plants under drought stress: A phenomic and molecular approach

Drought is one of the most significant abiotic stresses that limits the growth and productivity of crop plants. We investigated the physiological and molecular responses of tomato plants treated with Megafol® (Valagro S.p.A), under specific drought conditions. The goal was to evaluate the impact of Megafol®, a biostimulant composed of a complex of vitamins, aminoacids, proteins and betaines, in attenuating the negative physiological responses of drought. Tomato plants were grown in a greenhouse, and physiological parameters were collected using Scanalyzer 3D (LemnaTec, GmbH), a plant phenomics platform. Using this technology it is possible to dynamically study the effects of biostimulants, such as Megafol®, on plant development in terms of early detection of physiological plant stress responses. The results showed that drought-stressed plants treated with Megafol® were healthier in terms of the biomass produced and chlorophyll fluorescence, thus highlighting the higher tolerance to stress of the treated plants. The effects of Megafol® were also studied at a molecular level by analysing the induction of genes typically involved in drought stress responses. Our results demonstrate the efficacy of Megafol® to reduce drought-stress related damage in tomato plants