Plant cells encase themselves within a complex polysaccharide wall, which constitutes the raw material that is used to manufacture textiles, paper, lumber, films, thickeners and other products. The plant cell wall is also the primary source of cellulose, the most abundant and useful biopolymer on the Earth. The cell wall not only strengthens the plant body, but also has key roles in plant growth, cell differentiation, intercellular communication, water movement and defence. Recent discoveries have uncovered how plant cells synthesize wall polysaccharides, assemble them into a strong fibrous network and regulate wall expansion during cell growth.

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Growth of the plant cell wall

One of the defining features of plants is a body plan based on the physical properties of cell walls. Structural analyses of the polysaccharide components, combined with high-resolution imaging, have provided the basis for much of the current understanding of cell walls. The application of genetic methods has begun to provide new insights into how walls are made, how they are controlled, and how they function. However, progress in integrating biophysical, developmental, and genetic information into a useful model will require a system-based approach.

/pdf/toward-a-systems-approach-to-understanding-plant-cell-walls-375h7arxvl.pdf

Toward a Systems Approach to Understanding Plant Cell Walls

Maize (Zea mays L.) yields have risen continually wherever hybrid maize has been adopted, starting in the U.S. corn belt in the early 1930s. Plant breeding and improved management practices have produced this gain jointly. On average, about 50% of the increase is due to management and 50% to breeding. The two tools interact so closely that neither of them could have produced such progress alone. However, genetic gains may have to bear a larger share of the load in future years. Hybrid traits have changed over the years. Trait changes that increase resistance to a wide variety of biotic and abiotic stresses (e.g., drought tolerance) are the most numerous, but morphological and physiological changes that promote efficiency in growth, development, and partitioning (e.g., smaller tassels) are also recorded. Some traits have not changed over the years because breeders have intended to hold them constant (e.g., grain maturity date in U.S. corn belt). In other instances, they have not changed, despite breeders' intention to change them (e.g., harvest index). Although breeders have always selected for high yield, the need to select simultaneously for overall dependability has been a driving force in the selection of hybrids with increasingly greater stress tolerance over the years. Newer hybrids yield more than their predecessors in unfavorable as well as favorable growing conditions. Improvement in the ability of the maize plant to overcome both large and small stress bottlenecks, rather than improvement in primary productivity, has been the primary driving force of higher yielding ability of newer hybrid.

The Contribution of Breeding to Yield Advances in maize (Zea mays L.)

Cellulose microfibrils play essential roles in the organization of plant cell walls, thereby allowing a growth habit based on turgor. The fibrils are made by 30 nm diameter plasma membrane complexes composed of approximately 36 subunits representing at least three types of related CESA proteins. The complexes assemble in the Golgi, where they are inactive, and move to the plasma membrane, where they become activated. The complexes move through the plasma membrane during cellulose synthesis in directions that coincide with the orientation of microtubules. Recent, simultaneous, live-cell imaging of cellulose synthase and microtubules indicates that the microtubules exert a direct influence on the orientation of cellulose deposition. Genetic studies in Arabidopsis have identified a number of genes that contribute to the overall process of cellulose synthesis, but the role of these proteins is not yet known.

Cellulose Synthesis in Higher Plants

Plant cell walls represent the most abundant renewable resource on this planet. Despite their great abundance, only 2% of this resource is currently used by humans. Hence, research into the feasibility of using plant cell walls in the production of cost-effective biofuels is desirable. The main bottleneck for using wall materials is the recalcitrance of walls to efficient degradation into fermentable sugars. Manipulation of the wall polysaccharide biosynthetic machinery or addition of wall structure-altering agents should make it possible to tailor wall composition and architecture to enhance sugar yields upon wall digestion for biofuel fermentation. Study of the biosynthetic machinery and its regulation is still in its infancy and represents a major scientific and technical research challenge. Of course, any change in wall structure to accommodate cost-efficient biofuel production may have detrimental effects on plant growth and development due to the diverse roles of walls in the life of a plant. However, the diversity and abundance of wall structures present in the plant kingdom gives hope that this challenge can be met.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1365-313X.2008.03463.x

Cell‐wall carbohydrates and their modification as a resource for biofuels

Genes for the enzymes that make plant cell wall hemicellulosic polysaccharides remain to be identified. We report here the isolation of a complementary DNA (cDNA) clone encoding one such enzyme, mannan synthase (ManS), that makes the beta-1, 4-mannan backbone of galactomannan, a hemicellulosic storage polysaccharide in guar seed endosperm walls. The soybean somatic embryos expressing ManS cDNA contained high levels of ManS activities that localized to Golgi. Phylogenetically, ManS is closest to group A of the cellulose synthase-like (Csl) sequences from Arabidopsis and rice. Our results provide the biochemical proof for the involvement of the Csl genes in beta-glycan formation in plants.

https://science.sciencemag.org/content/sci/303/5656/363.full.pdf

Guar Seed ß-Mannan Synthase Is a Member of the Cellulose Synthase Super Gene Family

Stalk lodging in maize results in significant yield losses. We have determined that cellulose per unit length of the stalk is the primary determinant of internodal strength. An increase in cellulose concentration in the wall might allow simultaneous improvements in stalk strength and harvest index. Cellulose formation in plants can be perturbed by mutations in the genes involved in cellulose synthesis, post-synthetic cellulose alteration or deposition, N-glycosylation, and some other genes with as yet unknown functions. We have isolated 12 members of the cellulose synthase (CesA) gene family from maize. The genes involved in primary wall formation appear to have duplicated relatively independently in dicots and monocots. The deduced amino acid sequences of three of the maize genes, ZmCesA10–12, cluster with the Arabidopsis CesA sequences that have been shown to be involved in secondary wall formation. Based on their expression patterns across multiple tissues, these three genes appear to be coordinately expressed. The remaining genes show overlapping expression to varying degrees with ZmCesA1, 7, and 8 forming one group, ZmCesA3 and 5 a second group, and ZmCesA2 and 6 exhibiting independent expression of any other gene. This suggests that the varying levels of coexpression may just be incidental except in the case of ZmCesA10–12, which may interact with each other to form a functional enzyme complex. Isolation of the expressed CesA genes from maize and their association with primary or secondary wall formation has made it possible to test their respective roles in cellulose synthesis through mutational genetics or transgenic approaches. This information would be useful in improving stalk strength.

Cellulose synthesis in maize: isolation and expression analysis of the cellulose synthase (CesA) gene family

A device and method for applying a wind force to a plurality of plants in an agricultural environment is provided to screen for selected wind-resistance traits in the plurality of plants. In one embodiment of the present invention, a device is provided including a generating device for creating a moving fluid stream to provide the wind force, a directing device, such as a duct and/or movable vane, for precisely and selectively directing the wind force towards a portion of at least one plant, and a controller for adjusting one or more parameters of the fluid stream. The device and/or method embodiments of the present invention may thus be used to selectively apply the wind force to one or more plants (or portions thereof) such that the plants may be evaluated with respect to one or more wind-resistant physical characteristics.

Device and method for screening a plant population for wind damage resistance traits

A high throughput apparatus and method for gaining access to and extracting internal tissue or structure of interest from a seed or plurality of seed is disclosed. In one aspect, an apparatus utilizes means to expose the internal tissue or structure and means to separate at least some of the exposed internal tissue or structure for collection and evaluation. In one aspect, a method utilizes some force or action to expose the internal tissue or structure and some force or action to separate the internal tissue or structure.

Apparatus and methods to gain access to and extract intact immature embryo from developing maize kernels or specific internal tissue or structure from one or more seeds

The present device enables measurement of the susceptibility of corn plants to root lodging. The device is used to push over a corn stalk and the force used to push over the stalk, and the vibration of the stalk caused by the push are recorded. As material breaks in the stalk, an accelerometer, measures stalk vibration response to the breaking events; the data is then recorded to allow quantitative measurements of the susceptibility of corn plants to root lodging. This allows meaningful comparisons of various hybrids at early stages of hybrid evaluation and advancement.

Roberto Barreiro

Papers

Guar Seed ß-Mannan Synthase Is a Member of the Cellulose Synthase Super Gene Family

Cellulose synthesis in maize: isolation and expression analysis of the cellulose synthase (CesA) gene family

Device and method for screening a plant population for wind damage resistance traits

Apparatus and methods to gain access to and extract intact immature embryo from developing maize kernels or specific internal tissue or structure from one or more seeds

Correlating push force and stalk vibration to a plant's susceptibility to root lodging