Plant cells biosynthesize primary cell walls (PCW) in all cells and produce secondary cell walls (SCWs) in specific cell types that conduct water and/or provide mechanical support, such as xylem vessels and fibers. The characteristic mechanical stiffness, chemical recalcitrance, and hydrophobic nature of SCWs result from the organization of SCW-specific biopolymers, i.e., highly ordered cellulose, hemicellulose, and lignin. Synthesis of these SCW-specific biopolymers requires SCW-specific enzymes that are regulated by SCW-specific transcription factors. In this review, we summarize our current knowledge of the transcriptional regulation of SCW formation in plant cells. Advances in research on SCW biosynthesis during the past decade have expanded our understanding of the transcriptional regulation of SCW formation, particularly the functions of the NAC and MYB transcription factors. Focusing on the NAC-MYB-based transcriptional network, we discuss the regulatory systems that evolved in land plants to modify the cell wall to serve as a key component of structures that conduct water and provide mechanical support.

Starch within the endosperm of most species of the Triticeae has a unique bimodal granule morphology comprising large lenticular A-type granules and smaller near-spherical B-type granules. However, a few wild wheat species (Aegilops) are known to lack B-granules. Ae. peregrina and a synthetic tetraploid Aegilops with the same genome composition (SU) were found to differ in B-granule number. The synthetic tetraploid had normal A- and B-type starch granules whilst Ae. peregrina had only A-granules because the B-granules failed to initiate. A population segregating for B-granule number was generated by crossing these two accessions and was used to study the genetic basis of B-granule initiation. A combination of Bulked Segregant Analysis and QTL mapping identified a major QTL located on the short arm of chromosome 4S that accounted for 44.4% of the phenotypic variation. The lack of B-granules in polyploid Aegilops with diverse genomes suggests that the B-granule locus has been lost several times independently during the evolution of the Triticeae. It is proposed that the B-granule locus is susceptible to silencing during polyploidization and a model is presented to explain the observed data based on the assumption that the initiation of B-granules is controlled by a single major locus per haploid genome.

The last decade has witnessed dramatic changes in global food consumption patterns mainly because of population growth and economic development. Food substitutions for healthier eating, such as swapping regular servings of meat for protein-rich crops, is an emerging diet trend that may shape the future of food systems and the environment worldwide. To meet the erratic consumer demand in a rapidly changing world where resources become increasingly scarce due largely to anthropogenic activity, the need to develop crops that benefit both human health and the environment has become urgent. Legumes are often considered to be affordable plant-based sources of dietary proteins. Growing legumes provides significant benefits to cropping systems and the environment because of their natural ability to perform symbiotic nitrogen fixation, which enhances both soil fertility and water-use efficiency. In recent years, the focus in legume research has seen a transition from merely improving economically important species such as soybeans to increasingly turning attention to some promising underutilized species whose genetic resources hold the potential to address global challenges such as food security and climate change. Pulse crops have gained in popularity as an affordable source of food or feed; in fact, the United Nations designated 2016 as the International Year of Pulses, proclaiming their critical role in enhancing global food security. Given that many studies have been conducted on numerous underutilized pulse crops across the world, we provide a systematic review of the related literature to identify gaps and opportunities in pulse crop genetics research. We then discuss plausible strategies for developing and using pulse crops to strengthen food and nutrition security in the face of climate and anthropogenic changes.

Type 2C protein phosphatase (PP2C) is a central player in abscisic acid (ABA) signaling transduction, which is required for plant growth, development and stress responses. In Arabidopsis, group A PP2Cs inhibit activity of the SNF1-related protein kinases 2 (SnRK2) family via physical interaction. To clarify whether this scheme is conserved in woody plants, we experimentally isolated the genes homologous to three members of group A PP2Cs (PtABI1, PtAHG1 and PtAHG3) and 12 SnRK2s (PtSnRK2.1-2.12) from a model tree Populus trichocarpa, and examined their interaction using a yeast two-hybrid assay. Our results showed that only three PtSnRK2 proteins had a positive interaction with PtPP2Cs: PtSnRK2.10 possessed strong interaction activity with all three PtPP2Cs, while significant, but relatively weak, interactions were observed with PtSnRK2.6 and PtSnRK2.9. These three PtSnRK proteins are grouped into subclass 2 or 3, which are considered to be ABA-dependent kinases in Arabidopsis. These findings suggest that physical interaction between SnRK2 and PP2C is also conserved in poplars and may be involved in the ABA signaling pathway in tree plants.

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The Tracheary Element Differentiation-Related6 (TED6) and TED7 membrane proteins function in the differentiation of xylem vessel elements, the cellular units for water conduction in angiosperm plants. Functional analysis of TED6 and TED7 had suggested that these proteins directly bind to a subunit of the secondary cell wall (SCW)-related cellulose synthase complex, to promote SCW formation in xylem vessel elements. However, whether TED6 and TED7 function in SCW formation of xylem vessel elements only, or function broadly in other cell types has remained unclear. To clarify this, we conducted detailed expression analysis of TED6 and TED7 genes in Arabidopsis thaliana. This showed that TED6 and TED7 are expressed in differentiating vessel elements of all organs examined here, including roots, leaves, and inflorescence stems. We detected no TED6 and TED7 promoter activity in other types of cells with SCW thickening, such as fiber cells and anther endothecium, indicating that TED6 and TED7 have specific roles in SCW formation of vessel elements. Homology searches identified TED6/7-like proteins only in the angiosperm lineage. These data suggest that development of TED6/7 proteins could have coincided with the emergence of the angiosperm lineage, and that TED6/7 may have made key contributions to the evolution of water-conducting cells from tracheids to vessels.

An experiment was conducted to investigate the effects of different shading regimes [i.e., 60% (heavy), 30% (moderate), and 0% (control)] on 25 traits associated with the morphological features, photosynthetic gas exchange and agronomic characteristics of winged bean (Psophocarpus tetragonolobus), an underutilized protein-rich legume from the tropics. Collectively, 80% of the studied variables displayed significant differences (P<0.05) between at least two shade treatments. Shading generally showed most pronounced effect on the physiological traits of the legume, whereby the stomatal conductance, photosynthetic and transpiration rate differed significantly among plants for all treatments. The non-shaded plants were observed to have superior growth and physiological responses than the shaded plants. Interestingly, the moderately shaded plants exhibited the highest yield per plant, which significantly differed from the non-shaded and heavily shaded plants. This indicated that winged bean can adapt to partial canopy cover, making it a potential nitrogen-fixing cash crop which can be planted together with fruit or oil trees in commercial plantations.

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