In the majority of agricultural growing regions, crop production is highly dependent on the supply of exogenous nitrogen (N) fertilizers. Traditionally, this dependency and the use of N-fertilizers to restore N depleted soils has been rewarded with increased plant health and yields. In recent years, increased competition for non-renewable fossil fuel reserves has directly elevated prices of N-fertilizers and the cost of agricultural production worldwide. Furthermore, N-fertilizer based pollution is becoming a serious issue for many regions where agriculture is highly concentrated. To help minimize the N footprint associated with agricultural production there is significant interest at the plant level to develop technologies which can allow economically viable production while using less applied N. To complement recent reviews examining N utilization efficiency in agricultural plants, this review will explore those strategies operating specifically at the root level, which may directly contribute to improved N use efficiencies in agricultural crops such as cereals, where the majority of N-fertilizers are used and lost to the environment. Root specific phenotypes that will be addressed in the context of improvements to N acquisition and assimilation efficiencies include: root morphology; root to shoot ratios; root vigour, root length density; and root N transport and metabolism.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1365-3040.2009.02011.x

Root based approaches to improving nitrogen use efficiency in plants

Genes controlling hormone levels have been used to increase grain yields in wheat (Triticum aestivum) and rice (Oryza sativa). We created transgenic rice plants expressing maize (Zea mays), rice, or Arabidopsis thaliana genes encoding sterol C-22 hydroxylases that control brassinosteroid (BR) hormone levels using a promoter that is active in only the stems, leaves, and roots. The transgenic plants produced more tillers and more seed than wild-type plants. The seed were heavier as well, especially the seed at the bases of the spikes that fill the least. These phenotypic changes brought about 15 to 44% increases in grain yield per plant relative to wild-type plants in greenhouse and field trials. Expression of the Arabidopsis C-22 hydroxylase in the embryos or endosperms themselves had no apparent effect on seed weight. These results suggested that BRs stimulate the flow of assimilate from the source to the sink. Microarray and photosynthesis analysis of transgenic plants revealed evidence of enhanced CO2 assimilation, enlarged glucose pools in the flag leaves, and increased assimilation of glucose to starch in the seed. These results further suggested that BRs stimulate the flow of assimilate. Plants have not been bred directly for seed filling traits, suggesting that genes that control seed filling could be used to further increase grain yield in crop plants.

/pdf/brassinosteroids-regulate-grain-filling-in-rice-4okebo18mp.pdf

Brassinosteroids regulate grain filling in rice.

Cell walls are dynamic structures that represent key determinants of overall plant form, plant growth and development, and the responses of plants to environmental and pathogen-induced stresses. Walls play centrally important roles in the quality and processing of plant-based foods for both human and animal consumption, and in the production of fibres during pulp and paper manufacture. In the future, wall material that constitutes the major proportion of cereal straws and other crop residues will find increasing application as a source of renewable fuel and composite manufacture. Although the chemical structures of most wall constituents have been defined in detail, the enzymes involved in their synthesis and remodelling remain largely undefined, particularly those involved in polysaccharide biosynthesis. There have been real recent advances in our understanding of cellulose biosynthesis in plants, but, with few exceptions, the identities and modes of action of polysaccharide synthases and other glycosyltransferases that mediate the biosynthesis of the major non-cellulosic wall polysaccharides are not known. Nevertheless, emerging functional genomics and molecular genetics technologies are now allowing us to re-examine the central questions related to wall biosynthesis. The availability of the rice, Populus trichocarpa and Arabidopsis genome sequences, a variety of mutant populations, high-density genetic maps for cereals and other industrially important plants, high-throughput genome and transcript analysis systems, extensive publicly available genomics resources and an increasing armoury of analysis systems for the definition of candidate gene function will together allow us to take a systems approach to the description of wall biosynthesis in plants.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1467-7652.2005.00169.x

Plant cell wall biosynthesis: genetic, biochemical and functional genomics approaches to the identification of key genes.

Plant roots have a large range of functions, including acquisition of water and nutrients, as well as structural support Dissecting the genetic and molecular mechanisms controlling rice root development is critical for the development of new rice ideotypes that are better adapted to adverse conditions and for the production of sustainably achieved rice yield potential Most knowledge regarding the gene networks involved in root development has been accumulated in the model dicotyledon plant species Arabidopsis thaliana Rice, the model monocotyledon species, presents several singularities compared to A thaliana, including a root architecture characterized by a fibrous root system comprising five types of embryonic and postembryonic roots The anatomy and morphology of the rice root system, which is typical for a cereal, differs from that of A thaliana, for instance, by the presence of a lysigenous cortex and additional cell layers compared to the dicotyledon model Moreover, the structure and functions of the root apical meristem (RAM) of rice are distinct from those of A thaliana Recently, several rice root mutants have been identified via forward or reverse genetics, and these will aid in forming hypothesis to characterize either the divergence or conservation of genetic pathways relative to A thaliana Furthermore, these mutants will help to identify key genes in rice roots that may be missing in A thaliana This review summarizes both classical and recent data concerning the molecular genetics of rice root development, including root anatomy and morphology, RAM structure, RAM patterning, and root mutants

/pdf/molecular-genetics-of-rice-root-development-3a42pxkwnw.pdf

Molecular Genetics of Rice Root Development

Several vector systems are available for tissue-specific transactivation or chemical induction of transgene expression in plants. The choice facing researchers is which promoter system to commit to as this determines the range and characteristics of the expression resources available. The decision will not be the same for all species or applications. We present some general discussion on the use of these technologies and review in detail the properties in various (mainly angiosperm) species of the most promising: mGal4:VP16/UAS and pOp/LhG4 for transactivation, and the alc-switch, GVE/VGE, GVG, pOp6/LhGR, and XVE systems for chemical induction.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1365-313X.2006.02660.x

Transactivated and chemically inducible gene expression in plants.

We used enhancer trapping with the GAL4 transcriptional activator from yeast to obtain spatial control of transgene expression in all organs of the model monocotyledonous species rice (Oryza sativa L. cv. Nipponbare). Our T-DNA enhancer trapping cassette consisted of two principle components: (1) the minimal promoter-equipped gal4 gene placed adjacent to the right border, and (2) the green fluorescent protein gene (gfp) fused to the upstream activation sequence element (UAS) to which GAL4 binds and activates expression, so that gfp expression corresponds to gal4 expression. Agrobacterium-mediated integration of the cassette into the rice genome often brings the gal4 gene under transcriptional control of local genomic enhancers and promoters, resulting in gal4/gfp expression patterns ranging in specificity from single-cell types to constitutive expression. We produced more than 13 000 enhancer trap lines with this cassette and screened T(0) adult plants (1982 lines), T(1) seed (2684 lines) and T(1) seedlings (2667 lines) for gfp expression. Approximately 30% of the lines produced GFP, and we identified lines with gfp expression in specific cell types of all major organs of the rice plant. Subsequently, using the GUS reporter gene (uidA), we demonstrated that UAS:geneX constructs can be transactivated in specific cell types where gal4 and gfp are expressed, thus providing an excellent system for the manipulation of gene expression and physiological function in specific cell types of rice.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1365-313X.2005.02339.x

Emmanuel Guiderdoni

Papers

Spatial control of transgene expression in rice (Oryza sativa L.) using the GAL4 enhancer trapping system