Function of pea amino acid permease AAP6 in nodule nitrogen metabolism and export, and plant nutrition.[Pubmed: 30113690]

Legumes fix atmospheric nitrogen through a symbiotic relationship with bacteroids in root nodules. Following fixation in pea (Pisum sativum L.) nodules, nitrogen is reduced to amino acids that are exported via the nodule xylem to the shoot, and in the phloem to roots in support of growth. However, the mechanisms involved in amino acid movement towards the nodule vasculature, and their importance for nodule function and plant nutrition, were unknown. We found that in pea nodules the apoplasmic pathway is an essential route for amino acid partitioning from infected cells to the vascular bundles, and that amino acid permease PsAAP6 is a key-player in nitrogen retrieval from the apoplasm into inner cortex cells for nodule export. Using a microRNA-interference (miR) approach it was demonstrated that PsAAP6 function in nodules, and probably in roots, affects both shoot and root nitrogen supply, which were strongly decreased in PsAAP6-miR plants. Further, reduced transporter function resulted in increased nodule levels of ammonium, asparagine and other amino acids. Surprisingly, nitrogen fixation and nodule metabolism were upregulated in PsAAP6-miR plants indicating that under shoot nitrogen deficiency, or when plant nitrogen demand is high, systemic signaling leads to an increase in nodule activity, independent of the nodule nitrogen status.

Comparison of intracellular location and stimulus reaction times of forisomes in sieve tubes of four legume species.[Pubmed: 30111246]

Forisomes in legumes are responsible for fast sieve-element occlusion in response to injury to the vascular system. This prevents uncontrolled leakage of phloem sap and protects against invasion of pathogens. Here we compared forisomes of four different legumes (Pisum sativum, Vicia faba, Trifolium pratense and Medicago sativa) by their location (basal, central, apical) in the sieve element and reactivity to a distant heat stimulus. In each species, the majority of forisomes was located basally. Yet, we found differences in intracellular location: forisomes are distributed more evenly in the sieve elements of Pisum. After burning, basally located forisomes of the four species reacted with dispersion, followed by a spontaneous recondensation with similar reaction times. The results suggest universal forisome behaviour in fabacean species.

Development and characterization of penta-flowering and triple-flowering genotypes in garden pea (Pisum sativum L. var. hortense).[Pubmed: 30059526]

This study reports the development of a garden pea genotype 'VRPM-901-5' producing five flowers per peduncle at multiple flowering nodes, by using single plant selection approach from a cross 'VL-8 × PC-531'. In addition, five other stable genetic stocks, namely VRPM-501, VRPM-502, VRPM-503, VRPM-901-3 and VRPSeL-1 producing three flowers per peduncle at multiple flowering nodes were also developed. All these unique genotypes were of either mid- or late- maturity groups. Furthermore, these multi-flowering genotypes were identified during later generations (F4 onward), which might be because of fixation of certain QTLs or recessive gene combinations. Surprisingly, a common parent PC-531, imparting multi-flowering trait in ten cross combinations was identified. Thus, the genotype PC-531 seems to harbor some recessive gene(s) or QTLs that in certain combination(s) express the multi-flowering trait. The interaction between genotype and environment showed that temperature (11-20°C) plays a key role in expression of the multi-flowering trait besides genetic background. Furthermore, the possible relationship between various multi-flowering regulatory genes such as FN, FNA, NEPTUNE, SN, DNE, HR and environmental factors was also explored, and a comprehensive model explaining the multi-flowering trait in garden pea is proposed.

Functional Genomics and Genetic Control of Compound Leaf Development in Medicago truncatula: An Overview.[Pubmed: 30043306]

Diverse forms of leaves are present in nature. However, the regulatory mechanisms that underpin the development of diverse leaf forms remain enigmatic. The initiation of leaf primordia from the periphery of shoot apical meristem (SAM) requires downregulation of the class 1 knotted-like homeobox KNOXI proteins. In plants with simple leaves, this downregulation is permanent, consistent with leaves being determinant organs. In most of plants with compound leaves, the KNOXI proteins are reactivated in developing leaf primordia, and this reactivation is required for the development of compound leaves in these plants. Surprisingly, in Medicago truncatula and pea (Pisum sativum) that belong to the so-called inverted repeat-lacking clade (IRLC) of legume plants, the KNOXI proteins are not reactivated in leaf primordia and therefore not likely involved in the development of compound leaves in these plants. Instead, the legume FLORICAULA/LEAFY orthologues, UNIFOLIATA (UNI) and SINGLE LEAFLET1 (SGL1), are required for the initiation and development of lateral leaflet primordia in pea and M. truncatula plants, respectively. On the other hand, PALMATE-LIKE PENTAFOLIATA1 (PALM1) encoding a novel Cys(2)His(2) zinc finger transcription factor is required to suppress a morphogenetic activity at the leaf margin by negatively regulating SGL1 gene expression, and FUSED COMPOUND LEAF1 (FCL1) encoding a class M KNOX protein is required for the development of the leaf proximo-distal axis and organ boundary separation in M. truncatula. Thus, these recent studies have shown that SGL1/UNI, FCL1, and PALM1 provide a genetic framework for our understanding of compound leaf development in the legume plants.

Role of a receptor-like kinase K1 in pea Rhizobium symbiosis development.[Pubmed: 30043288]

The LysM receptor-like kinase K1 is involved in regulation of pea-rhizobial symbiosis development. The ability of the crop legume Pisum sativum L. to perceive the Nod factor rhizobial signals may depend on several receptors that differ in ligand structure specificity. Identification of pea mutants defective in two types of LysM receptor-like kinases (LysM-RLKs), SYM10 and SYM37, featuring different phenotypic manifestations and impaired at various stages of symbiosis development, corresponds well to this assumption. There is evidence that one of the receptor proteins involved in symbiosis initiation, SYM10, has an inactive kinase domain. This implies the presence of an additional component in the receptor complex, together with SYM10, that remains unknown. Here, we describe a new LysM-RLK, K1, which may serve as an additional component of the receptor complex in pea. To verify the function of K1 in symbiosis, several P. sativum non-nodulating mutants in the k1 gene were identified using the TILLING approach. Phenotyping revealed the blocking of symbiosis development at an appropriately early stage, strongly suggesting the importance of LysM-RLK K1 for symbiosis initiation. Moreover, the analysis of pea mutants with weaker phenotypes provides evidence for the additional role of K1 in infection thread distribution in the cortex and rhizobia penetration. The interaction between K1 and SYM10 was detected using transient leaf expression in Nicotiana benthamiana and in the yeast two-hybrid system. Since the possibility of SYM10/SYM37 complex formation was also shown, we tested whether the SYM37 and K1 receptors are functionally interchangeable using a complementation test. The interaction between K1 and other receptors is discussed.

MtNODULE ROOT1 and MtNODULE ROOT2 are essential for indeterminate nodule identity.[Pubmed: 30026291]

Symbiotic interactions between legume plants and rhizobia result in the formation of nitrogen-fixing nodules, but the molecular actors and the mechanisms allowing for the maintenance of nodule identity are poorly understood. Medicago truncatula NODULE ROOT1 (MtNOOT1), Pisum sativum COCHLEATA1 (PsCOCH1) and Lotus japonicus NOOT-BOP-COCH-LIKE1 (LjNBCL1) are orthologs of Arabidopsis (Arabidopsis thaliana) AtBLADE-ON-PETIOLE1/2 and are members of the NOOT-BOP-COCH-LIKE (NBCL) gene family, which has conserved roles in plant development and is essential for indeterminate and determinate nodule identity in legumes. The loss-of-function of MtNOOT1, PsCOCH1 and LjNBCL1 triggers a partial loss of nodule identity characterized by the development of ectopic roots arising from nodule vascular meristems. Here, we report the identification and characterization of a second gene involved in regulating indeterminate nodule identity in M. truncatula, MtNODULE ROOT2 (MtNOOT2). MtNOOT2 is the paralog of MtNOOT1 and belongs to a second legume-specific NBCL sub-clade, the NOOT-BOP-COCH-LIKE2 (NBCL2) clade. MtNOOT2 expression was induced during early nodule formation, and it was primarily expressed in the nodule central meristem. Mtnoot2 mutants did not present any particular symbiotic phenotype; however, the loss-of-function of both MtNOOT1 and MtNOOT2 resulted in the complete loss of nodule identity and was accompanied by drastic changes in the expression of symbiotic, defense, and root apical meristem marker genes. Mtnoot1 noot2 double mutants developed only non-fixing root-like structures that were no longer able to host symbiotic rhizobia. This study provides original insights into the molecular basis underlying nodule identity in legumes forming indeterminate nodules.

Interactive effect of 24-epibrassinolide and silicon alleviates cadmium stress via the modulation of antioxidant defense and glyoxalase systems and macronutrient content in Pisum sativum L. seedlings.[Pubmed: 30012086]

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Enhancing the systems productivity and water use efficiency through coordinated soil water sharing and compensation in strip-intercropping.[Pubmed: 30002422]

In arid areas, water shortage is threating agricultural sustainability, and strip-intercropping may serve as a strategy to alleviate the challenge. Here we show that strip-intercropping enhances the spatial distributions of soil water across the 0-110 cm rooting zones, improves the coordination of soil water sharing during the co-growth period, and provides compensatory effect for available soil water. In a three-year (2009-2011) experiment, shorter-season pea (Pisum sativum L.) was sown in alternate strips with longer-season maize (Zea mays L.) without or with an artificially-inserted root barrier (a solid plastic sheet) between the strips. The intercropped pea used soil water mostly in the top 20-cm layers, whereas maize plants were able to absorb water from deeper-layers of the neighboring pea strips. After pea harvest, the intercropped maize obtained compensatory soil water from the pea strips. The pea-maize intercropping without the root barrier increased grain yield by 25% and enhanced water use efficiency by 24% compared with the intercropping with the root barrier. The improvement in crop yield and water use efficiency was partly attributable to the coordinated soil water sharing between the inter-strips and the compensatory effect from the early-maturing pea to the late-maturing maize.