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Expansins are crucial components in plant cell walls and are classified into four subfamilies based on their sequences. To investigate their function differentiation in plant growth and stress resistance, four expansin subfamily genes— PtoEXPA8 , PtoEXPB3 , PtoEXLA2 , and PtoEXLB1 —were cloned from Populus tomentosa Carr. TC1521. Their sequence and structure exhibited typical subfamily characteristics. They were individually introduced in tobacco plants and made different contributions to the plants’ performances. Compared to wild-type plants, the PtoEXPA8 overexpressing lines increased the leaf area, and PtoEXPB3 facilitated floral organ development and earlier flowering and increased flower diameter. PtoEXLA2 increased plant height but reduced flower diameter and 1000-seeds weight. Finally, PtoEXLB1 increased plant height and decreased flower diameter. Under heat stress conditions, compared to the wild-type plants, the PtoEXPA8 overexpressing plants performed the best, while the other three genes barely contributed to heat resistance. The results indicate that the expansin subfamily genes underwent significant function differentiation, playing distinct roles in plant growth and stress resistance in poplar.

• Wheat is the most widely grown crop globally, providing 20% of all human calories and protein. Achieving step changes in genetic yield potential is crucial to ensure food security, but efforts are thwarted by an apparent trade-off between grain size and number. Expansins are proteins that play important roles in plant growth by enhancing stress relaxation in the cell wall, which constrains cell expansion. • Here, we describe how targeted overexpression of an α-expansin in early developing wheat seeds leads to a significant increase in grain size without a negative effect on grain number, resulting in a yield boost under field conditions. • The best-performing transgenic line yielded 12.3% higher average grain weight than the control, and this translated to an increase in grain yield of 11.3% in field experiments using an agronomically appropriate plant density. • This targeted transgenic approach provides an opportunity to overcome a common bottleneck to yield improvement across many crops.

The advent of user-friendly instruments for measuring force/deflection curves of plant surfaces at high spatial resolution has resulted in a recent outpouring of reports of the 'Young's modulus' of plant cell walls. The stimulus for these mechanical measurements comes from biomechanical models of morphogenesis of meristems and other tissues, as well as single cells, in which cell wall stress feeds back to regulate microtubule organization, auxin transport, cellulose deposition, and future growth directionality. In this article I review the differences between elastic modulus and wall extensibility in the context of cell growth. Some of the inherent complexities, assumptions, and potential pitfalls in the interpretation of indentation force/deflection curves are discussed. Reported values of elastic moduli from surface indentation measurements appear to be 10- to >1000-fold smaller than realistic tensile elastic moduli in the plane of plant cell walls. Potential reasons for this disparity are discussed, but further work is needed to make sense of the huge range in reported values. The significance of wall stress relaxation for growth is reviewed and connected to recent advances and remaining enigmas in our concepts of how cellulose, hemicellulose, and pectins are assembled to make an extensible cell wall. A comparison of the loosening action of α-expansin and Cel12A endoglucanase is used to illustrate two different ways in which cell walls may be made more extensible and the divergent effects on wall mechanics.

Cotton provides us the most important natural fibre. High fibre quality is the major goal of cotton breeding, and introducing genes conferring longer, finer and stronger fibre from Gossypium barbadense to Gossypium hirsutum is an important breeding strategy. We previously analysed the G. barbadense fibre development mechanism by gene expression profiling and found two homoeologous fibre‐specific α‐expansins from G. barbadense, GbEXPA2 and GbEXPATR. GbEXPA2 (from the DT genome) is a classical α‐expansin, while its homoeolog, GbEXPATR (AT genome), encodes a truncated protein lacking the normal C‐terminal polysaccharide‐binding domain of other α‐expansins and is specifically expressed in G. barbadense. Silencing EXPA in G. hirsutum induced shorter fibres with thicker cell walls. GbEXPA2 overexpression in G. hirsutum had no effect on mature fibre length, but produced fibres with a slightly thicker wall and increased crystalline cellulose content. Interestingly, GbEXPATR overexpression resulted in longer, finer and stronger fibres coupled with significantly thinner cell walls. The longer and thinner fibre was associated with lower expression of a number of secondary wall‐associated genes, especially chitinase‐like genes, and walls with lower cellulose levels but higher noncellulosic polysaccharides which advocated that a delay in the transition to secondary wall synthesis might be responsible for better fibre. In conclusion, we propose that α‐expansins play a critical role in fibre development by loosening the cell wall; furthermore, a truncated form, GbEXPATR, has a more dramatic effect through reorganizing secondary wall synthesis and metabolism and should be a candidate gene for developing G. hirsutum cultivars with superior fibre quality.

Plant-specific expansins were first discovered as pH-dependent cell-wall-loosening proteins involved in diverse physiological processes. No comprehensive analysis of the expansin gene family has yet been carried out at the whole genome level in Chinese jujube (Ziziphus jujuba Mill.). In this study, 30 expansin genes were identified in the jujube genome. These genes, which were distributed with varying densities across 10 of the 12 jujube chromosomes, could be divided into four subfamilies: 19 ZjEXPAs, 3 ZjEXPBs, 1 ZjEXLA, and 7 ZjEXLBs. Phylogenetic analysis of expansin genes in Arabidopsis, rice, apple, grape, and jujube classified these genes into 17 subgroups. Members of the same subfamily and subgroup shared conserved gene structure and motif compositions. Homology analysis identified 20 homologous gene pairs between jujube and Arabidopsis. Further analysis of ZjEXP gene promoter regions uncovered various growth, development and stress-responsive cis-acting elements. Expression analysis and transcript profiling revealed that ZjEXPs had different expression patterns in different tissues at various developmental stages. ZjEXPA4 and ZjEXPA6 were highly expressed in young fruits, ZjEXPA3 and ZjEXPA5 were significantly expressed in flowers, and ZjEXPA7 was specifically expressed in young leaves. The results of this study, the first systematic analysis of the jujube expansin gene family, can serve as a strong foundation for further elucidation of the physiological functions and biological roles of jujube expansin genes.

• Plants must rearrange the network of complex carbohydrates in their cell walls during normal growth and development. To accomplish this, all plants depend on proteins called expansins that nonenzymatically loosen noncovalent bonding between cellulose microfibrils. • Surprisingly, expansin genes have more recently been found in some bacteria and microbial eukaryotes, where their biological functions are largely unknown. • Here, we reconstruct a comprehensive phylogeny of microbial expansin genes. We find these genes in all eukaryotic microorganisms that have structural cell wall cellulose, suggesting expansins evolved in ancient marine microorganisms long before the evolution of land plants. We also find expansins in an unexpectedly high diversity of bacteria and fungi that do not have cellulosic cell walls. These bacteria and fungi inhabit varied ecological contexts, mirroring the diversity of terrestrial and aquatic niches where plant and/or algal cellulosic cell walls are present. • The microbial expansin phylogeny shows evidence of multiple horizontal gene transfer events within and between bacterial and eukaryotic microbial lineages, which may in part underlie their unusually broad phylogenetic distribution. Overall, expansins are unexpectedly widespread in bacteria and eukaryotes, and the contribution of these genes to microbial ecological interactions with plants and algae has probbaly been underappreciated.

Reducing the enzyme loadings for enzymatic saccharification of lignocellulose is required for economically feasible production of biofuels and biochemicals. One strategy is addition of small amounts of synergistic proteins to cellulase mixtures. Synergistic proteins increase the activity of cellulase without causing significant hydrolysis of cellulose. Synergistic proteins exert their activity by inducing structural modifications in cellulose. Recently, synergistic proteins from various biological sources, including bacteria, fungi, and plants, were identified based on genomic data, and their synergistic activities were investigated. Currently, an up-to-date overview of several aspects of synergistic proteins, such as their functions, action mechanisms and synergistic activity, are important for future industrial application. In this review, we summarize the current state of research on four synergistic proteins: carbohydrate-binding modules, plant expansins, expansin-like proteins, and Auxiliary Activity family 9 (formerly GH61) proteins. This review provides critical information to aid in promoting research on the development of efficient and industrially feasible synergistic proteins.

The growth of plant cells is inseparable from relaxation and expansion of cell walls. Expansins are a class of cell wall binding proteins, which play important roles in the relaxation of cell walls. Although there are many members in expansin gene family, the functions of most expansin genes in plant growth and development are still poorly understood. In this study, the functions of two expansin genes, AtEXPA4 and AtEXPB5 were characterized in Arabidopsis thaliana. AtEXPA4 and AtEXPB5 displayed consistent expression patterns in mature pollen grains and pollen tubes, but AtEXPA4 also showed a high expression level in primary roots. Two single mutants, atexpa4 and atexpb5, showed normal reproductive development, whereas atexpa4atexpb5 double mutant was defective in pollen tube growth. Moreover, AtEXPA4 overexpression enhanced primary root elongation, on the contrary, knocking out AtEXPA4 made the growth of primary root slower. Our results indicated that AtEXPA4 and AtEXPB5 were redundantly involved in pollen tube growth and AtEXPA4 was required for primary root elongation.

The discovery of microbial expansins emerged from studies of the mechanism of plant cell growth and the molecular basis of plant cell wall extensibility. Expansins are wall-loosening proteins that are universal in the plant kingdom and are also found in a small set of phylogenetically diverse bacteria, fungi, and other organisms, most of which colonize plant surfaces. They loosen plant cell walls without detectable lytic activity. Bacterial expansins have attracted considerable attention recently for their potential use in cellulosic biomass conversion for biofuel production, as a means to disaggregate cellulosic structures by nonlytic means (“amorphogenesis”). Evolutionary analysis indicates that microbial expansins originated by multiple horizontal gene transfers from plants. Crystallographic analysis of BsEXLX1, the expansin from Bacillus subtilis, shows that microbial expansins consist of two tightly packed domains: the N-terminal domain D1 has a double-ψ β-barrel fold similar to glycosyl hydrolase family-45 enzymes but lacks catalytic residues usually required for hydrolysis; the C-terminal domain D2 has a unique β-sandwich fold with three co-linear aromatic residues that bind β-1,4-glucans by hydrophobic interactions. Genetic deletion of expansin in Bacillus and Clavibacter cripples their ability to colonize plant tissues. We assess reports that expansin addition enhances cellulose breakdown by cellulase and compare expansins with distantly related proteins named swollenin, cerato-platanin, and loosenin. We end in a speculative vein about the biological roles of microbial expansins and their potential applications. Advances in this field will be aided by a deeper understanding of how these proteins modify cellulosic structures.

Background Expansins (EXPs) are important components of the plant cell wall. They are involved in plant growth and development and diverse environmental stress responses by promoting cell-wall loosening and cell enlargement. Although EXPs have been characterized in many plant species, little is known about the EXPs in Carya illinoinensis . Methods The CiEXP gene family was systematically analyzed using bioinformatics. RNA-seq data (both from our study and public databases) and qRT-PCR were employed to analyze the expression patterns of the CiEXP family in different tissues, under biotic and abiotic stress, and in persistent versus abscised fruit. Results In this study, a total of 39 EXP genes unevenly distributed on 14 chromosomes were identified in the C. illinoinensis genome, which were classified into four subfamilies (27 CiEXPAs, 3 CiEXPBs, 2 CiEXLAs, and 7 CiEXLBs), and the motif and gene structures were consistent with this subfamily classification. Thirty-six pairs of duplicated genes were identified, suggesting that gene duplication may have contributed to the expansion of the EXP gene family. Collinearity analysis provided further phylogenetic insights into the EXP gene family. Cis -acting element analysis revealed that the promoter regions of the CiEXPs gene were associated with hormone-responsive, plant growth and development, and stress-responsive, particularly ABA response element (ABRE) and MeJA-responsive element. The expression results showed that most CiEXPs exhibited tissue-specific expression patterns, and some CiEXPs were highly responsive to abiotic and biotic stresses. Additionally, most CiEXPA genes, CiEXPB1/2 , and CiEXLA2 were up-regulated in persistent fruit. Conclusions Our study findings enhance the understanding of the CiEXP gene family and facilitate the selection of suitable candidate genes for further study, which lays a foundation for future investigations into the functional roles of specific CiEXPs .