HighlightRecent research shows that sugar availability triggers bud outgrowth. This paper further demonstrates that the effect of sucrose involves changes in the hormonal network related to bud outgrowth, and identifies potential hormones involved in sugar control.

ORCID IDs: 0000-0002-0050-4001 (B.C.S.); 0000-0002-3526-7982 (J.L.); 0000-0001-7896-6049 (M.P.); 0000-0001-7144-1274 (D.X.); 0000-0001-5026-095X (S.Ci.); 0000-0002-6496-3792 (S.R.H.); 0000-0003-1808-5172 (V.P.).In the model plant Arabidopsis (Arabidopsis thaliana), endogenous and environmental signals acting on the shoot apical meristem cause acquisition of inflorescence meristem fate. This results in changed patterns of aerial development seen as the transition from making leaves to the production of flowers separated by elongated internodes. Two related BEL1-like homeobox genes, PENNYWISE (PNY) and POUND-FOOLISH (PNF), fulfill this transition. Loss of function of these genes impairs stem cell maintenance and blocks internode elongation and flowering. We show here that pny pnf apices misexpress lateral organ boundary genes BLADE-ON-PETIOLE1/2 (BOP1/2) and KNOTTED-LIKE FROM ARABIDOPSIS THALIANA6 (KNAT6) together with ARABIDOPSIS THALIANA HOMEOBOX GENE1 (ATH1). Inactivation of genes in this module fully rescues pny pnf defects. We further show that BOP1 directly activates ATH1, whereas activation of KNAT6 is indirect. The pny pnf restoration correlates with renewed accumulation of transcripts conferring floral meristem identity, including FD, SQUAMOSA PROMOTER-BINDING PROTEIN LIKE genes, LEAFY, and APETALA1. To gain insight into how this module blocks flowering, we analyzed the transcriptome of BOP1-overexpressing plants. Our data suggest a central role for the microRNA156-SQUAMOSA PROMOTER BINDING PROTEIN-LIKE-microRNA172 module in integrating stress signals conferred in part by promotion of jasmonic acid biosynthesis. These data reveal a potential mechanism by which repression of lateral organ boundary genes by PNY-PNF is essential for flowering.Plant development relies on the activity of the shoot apical meristem (SAM) as a continuous source of founder cells for production of new leaves, shoots, and internodes throughout the life cycle (for review, see Aichinger et al., 2012). A tight balance between the allocation of cells to developing primordia and the perpetuation of pluripotent stem cells in the central zone maintains the SAM at a constant size. In Arabidopsis (Arabidopsis thaliana), the vegetative SAM produces leaves in a spiral phyllotaxy with dormant axillary meristems. In conjunction, internode elongation is repressed, resulting in a basal rosette. The transition to flowering is governed by internal and external signals that converge at the SAM to promote acquisition of inflorescence meristem (IM) fate (for review, see Amasino and Michaels, 2010;Srikanth and Schmid, 2011;Andrés and Coupland, 2012). This process, known as floral evocation, results in new patterns of growth at the shoot apex, including production of flowers, and an increase in stem elongation, called bolting. Lateral organ boundaries are specialized domains of restricted growth that separate meristem and organ compartments and produce axillary meristems (for review, see Aida and Tasaka, 2006;Tian et al., 2014). Early in the transition t...

Summary Apical dominance occurs when the growing shoot tip inhibits the outgrowth of axillary buds. Apically‐derived auxin in the nodal stem indirectly inhibits bud outgrowth via cytokinins and strigolactones. Recently, sugar deprivation was found to contribute to this phenomenon. Using rose and pea, we investigated whether sugar availability interacts with auxin in bud outgrowth control, and the role of cytokinins and strigolactones, in vitro and in planta. We show that sucrose antagonises auxin’s effect on bud outgrowth, in a dose‐dependent and coupled manner. Sucrose also suppresses strigolactone inhibition of outgrowth and the rms3 strigolactone‐perception mutant is less affected by reducing sucrose supply. However, sucrose does not interfere with the regulation of cytokinin levels by auxin and stimulates outgrowth even with optimal cytokinin supply. These observations were assembled into a computational model in which sucrose represses bud response to strigolactones, largely independently of cytokinin levels. It quantitatively captures our observed dose‐dependent sucrose‐hormones effects on bud outgrowth and allows us to express outgrowth response to various combinations of auxin and sucrose levels as a simple quantitative law. This study places sugars in the bud outgrowth regulatory network and paves the way for a better understanding of branching plasticity in response to environmental and genotypic factors.

Pyoverdines are siderophores synthesized by fluorescent Pseudomonas spp. Under iron-limiting conditions, these high-affinity ferric iron chelators are excreted by bacteria in the soil to acquire iron. Pyoverdines produced by beneficial Pseudomonas spp. ameliorate plant growth. Here, we investigate the physiological incidence and mode of action of pyoverdine from Pseudomonas fluorescens C7R12 on Arabidopsis (Arabidopsis thaliana) plants grown under iron-sufficient or iron-deficient conditions. Pyoverdine was provided to the medium in its iron-free structure (apo-pyoverdine), thus mimicking a situation in which it is produced by bacteria. Remarkably, apo-pyoverdine abolished the iron-deficiency phenotype and restored the growth of plants maintained in the iron-deprived medium. In contrast to a P. fluorescens C7R12 strain impaired in apo-pyoverdine production, the wild-type C7R12 reduced the accumulation of anthocyanins in plants grown in iron-deficient conditions. Under this condition, apo-pyoverdine modulated the expression of around 2,000 genes. Notably, apo-pyoverdine positively regulated the expression of genes related to development and iron acquisition/redistribution while it repressed the expression of defense-related genes. Accordingly, the growth-promoting effect of apo-pyoverdine in plants grown under iron-deficient conditions was impaired in iron-regulated transporter1 and ferric chelate reductase2 knockout mutants and was prioritized over immunity, as highlighted by an increased susceptibility to Botrytis cinerea. This process was accompanied by an overexpression of the transcription factor HBI1, a key node for the cross talk between growth and immunity. This study reveals an unprecedented mode of action of pyoverdine in Arabidopsis and demonstrates that its incidence on physiological traits depends on the plant iron status.

Glutamine biosynthesis for N-remobilization and seed filling in Arabidopsis is mainly catalysed by the three major GS1 isoforms, GLN1;1, GLN1;2, and GLN1;3, which are localized in different-order veins in the leaves.

One-sentence summary: 40The loss-of-function of MtNOOT1 and MtNOOT2 leads to the complete loss of nodule identity, prevents 41 the symbiotic process, and results in the absence of nitrogen fixation in Medicago truncatula. 56VZ, SC, GEDO, and PR analyzed the data. KM, KS and PR wrote the article. 58This work was supported by the CNRS, by the grants ANR SVSE 6.2010.1 (LEGUMICS) and ANR-14- 62Agriculture (Dufrenoy Grant, 2011). This work has benefited from the facilities and expertise of the IMAGIF 63Cell Biology Unit of the Gif campus (www.imagif.cnrs.fr) which is supported by the Conseil Général de 64 l'Essonne. 66The author responsible for distribution of materials integral to the findings presented in this article in 67 accordance with the policy described in the instructions for authors (www.plantphysiol.org) is: Pascal 68 Ratet (pascal.ratet@u-psud.fr). 70 71 Acknowledgments 72The Institute of Plant Sciences Paris-Saclay (IPS2, France) benefits from the support of the LabEx Saclay 97fixing root-like structures that were no longer able to host symbiotic rhizobia. This study provides original 98 insights into the molecular basis underlying nodule identity in legumes forming indeterminate nodules. 100 INTRODUCTION 102The symbiotic interaction between legumes and rhizobia results in the formation of root nodules 103 dedicated to host nitrogen-fixing rhizobia. This unique ability to form root nodules is restricted to the 104 Rosids I clade. The predisposition of plants to enter symbiosis with nitrogen-fixing rhizobia seems to have 105 evolved once, between 70 and 100 million years ago and to have derived from an ancestral and 106 widespread symbiosis, the arbuscular mycorrhizal symbiosis (AMS, Soltis et al., 1995; Smith and Read, 107 2008;Bonfante and Genre, 2010;Humphreys et al., 2010;Werner et al., 2014). 109Genetic approaches using nodule-deficient (nod -) and non-functional nodule (fix -) mutant plants 110 allowed the identification of many genes essential for the early steps of root nodule symbiosis. 111Recognition between symbiotic partners, rhizobial infection and nodule organogenesis are initiated by the 112 host plant perception of rhizobial lipo-chitooligosacharidic compounds Jones et al., 113 2007;Kouchi et al., 2010; Horvath et al., 2011;Ovchinnikova et al., 2011; 114 . These compounds are called Nod factors 115and they are structurally similar to the mycorrhization factors (Myc factors) required for AMS initiation 116 (Maillet et al., 2011). 118In the Papilionaceae family, determinate nodules formed in the Phaseoleae, Loteae and 119Dalbergieae tribes have no persistent apical nodule meristem (NM). However, indeterminate nodules 120 formed in the Trifolieae and Fabeae tribes have a persistent apical NM. Indeterminate nodules are highly-121 structured and present different zones; the NM, the infection zone, the nitrogen fixation zone and the older 122 senescent zone (from top to bottom; . The ability of indeterminate nodules to grow 123 continuously results from the presence of the NM. ...

Chloroplasts can act as key players in the perception and acclimatization of plants to incoming environmental signals. A growing body of evidence indicates that chloroplasts play a critical role in plant immunity. Chloroplast function can be regulated by the nucleotides guanosine tetraphosphate and pentaphosphate [(p)ppGpp]. In plants, (p)ppGpp levels increase in response to abiotic stress and to plant hormones which are involved in abiotic and biotic stress signalling. In this study, we analysed the transcriptome of Arabidopsis plants that over-accumulate (p)ppGpp, and unexpectedly found a decrease in the levels of a broad range of transcripts for plant defence and immunity. To determine whether (p)ppGpp is involved in the modulation of plant immunity, we analysed the susceptibility of plants with different levels of (p)ppGpp to Turnip mosaic virus (TuMV) carrying a green fluorescent protein (GFP) reporter. We found that (p)ppGpp accumulation was associated with increased susceptibility to TuMV and reduced levels of the defence hormone salicylic acid (SA). In contrast, plants with lower (p)ppGpp levels showed reduced susceptibility to TuMV, and this was associated with the precocious up-regulation of defence-related genes and increased SA content. We have therefore demonstrated a new link between (p)ppGpp metabolism and plant immunity in Arabidopsis.

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