Regulatory 14-3-3 proteins activate the plant plasma membrane H(+)-ATPase by binding to its C-terminal autoinhibitory domain. This interaction requires phosphorylation of a C-terminal, mode III, recognition motif as well as an adjacent span of approximately 50 amino acids. Here we report the X-ray crystal structure of 14-3-3 in complex with the entire binding motif, revealing a previously unidentified mode of interaction. A 14-3-3 dimer simultaneously binds two H(+)-ATPase peptides, each of which forms a loop within the typical 14-3-3 binding groove and therefore exits from the center of the dimer. Several H(+)-ATPase mutants support this structure determination. Accordingly, 14-3-3 binding could result in H(+)-ATPase oligomerization. Indeed, by using single-particle electron cryomicroscopy, the 3D reconstruction of the purified H(+)-ATPase/14-3-3 complex demonstrates a hexameric arrangement. Fitting of 14-3-3 and H(+)-ATPase atomic structures into the 3D reconstruction map suggests the spatial arrangement of the holocomplex.

Typically, F 1 -hybrids are more vigorous than their homozygous, genetically distinct parents, a phenomenon known as heterosis. In the present study, the transcriptomes of the reciprocal maize (Zea mays L.) hybrids B733Mo17 and Mo173B73 and their parental inbred lines B73 and Mo17 were surveyed in primary roots, early in the developmental manifestation of heterotic root traits. The application of statistical methods and a suitable experimental design established that 34,233 (i.e., 86%) of all high-confidence maize genes were expressed in at least one genotype. Nearly 70% of all expressed genes were differentially expressed between the two parents and 42%-55% of expressed genes were differentially expressed between one of the parents and one of the hybrids. In both hybrids,~10% of expressed genes exhibited nonadditive gene expression. Consistent with the dominance model (i.e., complementation) for heterosis, 1124 genes that were expressed in the hybrids were expressed in only one of the two parents. For 65 genes, it could be shown that this was a consequence of complementation of genomic presence/absence variation. For dozens of other genes, alleles from the inactive inbred were activated in the hybrid, presumably via interactions with regulatory factors from the active inbred. As a consequence of these types of complementation, both hybrids expressed more genes than did either parental inbred. Finally, in hybrids,~14% of expressed genes exhibited allele-specific expression (ASE) levels that differed significantly from the parental-inbred expression ratios, providing further evidence for interactions of regulatory factors

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SUMMARYRoot hairs are instrumental for nutrient uptake in monocot cereals. The maize (Zea mays L.) roothairless5 (rth5) mutant displays defects in root hair initiation and elongation manifested by a reduced density and length of root hairs. Map-based cloning revealed that the rth5 gene encodes a monocot-specific NADPH oxidase. RNA-Seq, in situ hybridization and qRT-PCR experiments demonstrated that the rth5 gene displays preferential expression in root hairs but also accumulates to low levels in other tissues. Immunolocalization detected RTH5 proteins in the epidermis of the elongation and differentiation zone of primary roots. Because superoxide and hydrogen peroxide levels are reduced in the tips of growing rth5 mutant root hairs as compared with wild-type, and Reactive oxygen species (ROS) is known to be involved in tip growth, we hypothesize that the RTH5 protein is responsible for establishing the high levels of ROS in the tips of growing root hairs required for elongation. Consistent with this hypothesis, a comparative RNA-Seq analysis of 6-day-old rth5 versus wild-type primary roots revealed significant over-representation of only two gene ontology (GO) classes related to the biological functions (i.e. oxidation/reduction and carbohydrate metabolism) among 893 differentially expressed genes (FDR <5%). Within these two classes the subgroups 'response to oxidative stress' and 'cellulose biosynthesis' were most prominently represented.

A high-resolution proteome and phosphoproteome atlas of four maize (Zea mays) primary root tissues, the cortex, stele, meristematic zone, and elongation zone, was generated. High-performance liquid chromatography coupled with tandem mass spectrometry identified 11,552 distinct nonmodified and 2,852 phosphorylated proteins across the four root tissues. Two gradients reflecting the abundance of functional protein classes along the longitudinal root axis were observed. While the classes RNA, DNA, and protein peaked in the meristematic zone, cell wall, lipid metabolism, stress, transport, and secondary metabolism culminated in the differentiation zone. Functional specialization of tissues is underscored by six of 10 cortex-specific proteins involved in flavonoid biosynthesis. Comparison of this data set with high-resolution seed and leaf proteome studies revealed 13% (1,504/11,552) root-specific proteins. While only 23% of the 1,504 root-specific proteins accumulated in all four root tissues, 61% of all 11,552 identified proteins accumulated in all four root tissues. This suggests a much higher degree of tissue-specific functionalization of root-specific proteins. In summary, these data illustrate the remarkable plasticity of the proteomic landscape of maize primary roots and thus provide a starting point for gaining a better understanding of their tissue-specific functions.

The numerous feedback loops between roots, microorganisms, soil chemical and physical properties, and environmental variables result in spatial parameter patterns which are highly dynamic in time. In order to improve our understanding of the related rhizosphere processes and their relevance at the soil–plant system scale, experimental platforms are required. Those platforms should enable (1) to relate small scale observations (nm to dm) to system behaviour, (2) the integration of physical, chemical and biological sampling approaches within the same experiment, and (3) sampling at different time points during the life cycle of the system in question. Here we describe what requirements have to be met and to what extent this has been achieved in practice by the experimental platforms which were set up within the framework of DFG priority programme 2089 “Rhizosphere Spatiotemporal Organisation—a key to rhizosphere functions”. It is discussed to what extent theoretical considerations could be accommodated, in particular for the comparison across scales, i.e., from laboratory to field scale. The latter scale is of utmost importance to overcome the trade‐off between fraction of life cycle covered and the avoidance of unrealistic root length densities.

HighlightMaize primary root tissues display extensive transcriptomic plasticity upon water deficit. The most significant adaptive changes in the elongation zone lead to reprogramming of metabolism and cell wall organization.

The diversity of maize (Zea mays) is the backbone of modern heterotic patterns and hybrid breeding. Historically, US farmers exploited this variability to establish today's highly productive Corn Belt inbred lines from blends of dent and flint germplasm pools. Here, we report de novo genome sequences of four European flint lines assembled to pseudomolecules with scaffold N50 ranging from 6.1 to 10.4 Mb. Comparative analyses with two US Corn Belt lines explains the pronounced differences between both germplasms. While overall syntenic order and consolidated gene annotations reveal only moderate pangenomic differences, whole-genome alignments delineating the core and dispensable genome, and the analysis of heterochromatic knobs and orthologous long terminal repeat retrotransposons unveil the dynamics of the maize genome. The high-quality genome sequences of the flint pool complement the maize pangenome and provide an important tool to study maize improvement at a genome scale and to enhance modern hybrid breeding.