Plant expansins: diversity and interactions with plant cell walls

Results from various expansin related studies have demonstrated that expansins present an opportunity to improve various crops in many different aspects ranging from yield and fruit ripening to improved stress tolerance.
 The recent advances in expansin studies were reviewed. Besides producing the strength that is needed by the plants, cell walls define cell shape, cell size and cell function. Expansins are cell wall proteins which consist of four sub families; α-expansin, β-expansin, expansin-like A and expansin-like B. These proteins mediate cell wall loosening and they are present in all plants and in some microbial organisms and other organisms like snails. Decades after their initial discovery in cucumber, it is now clear that these small proteins have diverse biological roles in plants. Through their ability to enable the local sliding of wall polymers by reducing adhesion between adjacent wall polysaccharides and the part they play in cell wall remodeling after cytokinesis, it is now clear that expansins are required in almost all plant physiological development aspects from germination to fruiting. This is shown by the various reports from different studies using various molecular biology approaches such as gene achieve these many roles through their non-enzymatic wall loosening ability. This paper reviews and summarizes some of the reported functions of expansins and outlines the potential uses of expansins in crop improvement programs.

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Expansins: roles in plant growth and potential applications in crop improvement

Drought stress delays endosperm development and misregulates genes associated with cytoskeleton organization and grain quality proteins in developing wheat seeds

Expansins are pH-dependent cell wall loosening proteins which form a large family in plants. They have been shown to be involved in various developmental processes and been implicated in enabling plants' ability to absorb nutrients from the soil as well as conferring biotic and abiotic stress resistances. It is therefore clear that they can be potential targets in genetic engineering for crop improvement. Tobacco (Nicotiana tabacum) is a major crop species as well as a model organism. Considering that only a few tobacco expansins have been studied, a genome-wide analysis of the tobacco expansin gene family is necessary. In this study, we identified 52 expansins in tobacco, which were classified into four subfamilies: 36 NtEXPAs, 6 NtEXPBs, 3 NtEXLAs and 7 NtEXLBs. Compared to other species, the NtEXLB subfamily size was relatively larger. Phylogenetic analysis showed that the 52 tobacco expansins were divided into 13 subgroups. Gene structure analysis revealed that genes within subfamilies/subgroups exhibited similar characteristics such as gene structure and protein motif arrangement. Whole-genome duplication and tandem duplication events may have played important roles in the expanding of tobacco expansins. Cis-Acting element analysis revealed that each expansin gene was regulated or several expansin genes were co-regulated by both internal and environmental factors. 35 of these genes were identified as being expressed according to a microarray analysis. In contrast to most NtEXPAs which had higher expression levels in young organs, NtEXLAs and NtEXLBs were preferentially expressed in mature or senescent tissues, suggesting that they might play different roles in different organs or at different developmental stages. As the first step towards genome-wide analysis of the tobacco expansin gene family, our work provides solid background information related to structure, evolution and expression as well as regulatory cis-acting elements of the tobacco expansins. This information will provide a strong foundation for cloning and functional exploration of expansin genes in tobacco.

Genome-wide identification of the expansin gene family in tobacco (Nicotiana tabacum).

Plant expansins are capable of inducing pH-dependent cell wall extension and stress relaxation. They may be useful as targets for crop improvement to enhance fruit development and stress resistance. Tomato is a major agricultural crop and a model plant for studying fruit development. Because only some tomato expansins have been studied, a genome-wide analysis of the tomato expansin family is necessary. In this study, we identified 25 SlEXPAs, eight SlEXPBs, one SlEXLA, four SlEXLBs, and five short homologs in the tomato genome. 25 of these genes were identified as being expressed. Bioinformatic analysis showed that although tomato expansins share similarities with those from other plants, they also exhibit specific features regarding genetic structure and amino acid sequences, which indicates a unique evolutionary process. Segmental and tandem duplication events have played important roles in expanding the tomato expansin family. Additionally, the 3-exon/2-intron structure may form the basic organization of expansin genes. We identified new expansin genes preferentially expressed in fruits (SlEXPA8, SlEXPB8, and SlEXLB1), roots (SlEXPA9, SlEXLB2, and SlEXLB4), and floral organs. Among the analyzed genes those that were inducible by hormone or stress treatments, including SlEXPA3, SlEXPA7, SlEXPB1-B2, SlEXPB8, SlEXLB1-LB2, and SlEXLB4. Our findings may further clarify the biological activities of tomato expansins, especially those related to fruit development and stress resistance, and contribute to the genetic modification of tomato plants to improve crop quality and yield.

Genome-wide identification and expression analysis of the expansin gene family in tomato.

By promoting cell wall loosening, expansins contribute to cell enlargement during various developmental processes. Nevertheless, the role of expansins in the expansion and development of endosperm—a major seed component whose cell size is significantly associated with grain yield—is poorly understood. To explore associated biological processes and the evolution of expansins in maize, we performed a systematic analysis of the expansin gene family encompassing gene structure, phylogeny, chromosomal location, gene duplication, and gene ontology. A total of 88 maize expansin genes (ZmEXPs) were identified and categorized into three subfamilies according to their phylogenetic relationships. Expression patterns of ZmEXPs were also investigated in nine different tissues by semi-quantitative RT-PCR. The expression of eight ZmEXPs was detected in endosperm, with five showing endosperm-specific expression. Quantitative RT-PCR was used to analyze expression patterns of the eight ZmEXPs in endosperm (10 days after pollination) under abscisic acid (ABA) and gibberellic acid (GA3) treatments. All eight ZmEXPs were found to be significantly regulated by ABA and GA3 in endosperm, suggesting important roles for these hormones in the regulation of ZmEXPs during endosperm development. Our results provide essential information for ZmEXPs cloning and functional exploration, which will assist research on expansin-related mechanisms and contribute to future enhancement of maize grain yield.

Genome-wide identification and characterization of maize expansin genes expressed in endosperm.

Background
Intronless genes are a feature of prokaryotes; however, they are widespread and unequally distributed among eukaryotes and represent an important resource to study the evolution of gene architecture. Although many databases on exons and introns exist, there is currently no cohesive database that collects intronless genes in plants into a single database.

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PIGD: a database for intronless genes in the Poaceae

The ZmDULL1 gene encodes a starch synthase and is a determinant of the structure of endosperm starch in maize (Zea mays L.). However, little is known regarding the regulatory mechanism of the ZmDULL1 gene. In this study, we isolated and characterized the ZmDULL1 promoter (PDULL1), which is the 5' flanking region of ZmDULL1 in maize. Sequence analysis showed that several cis-acting elements important for endosperm expression (GCN4_motif and AACA-element) were located within the promoter. A series of PDULL1 deletion derivatives, PDULL1-1-PDULL1-4, from the translation start code (-1676, -1216, -740, and -343) were fused to the β-glucuronidase (GUS) reporter gene. Each deletion construct was transformed into rice using the Agrobacterium-mediated method, and then GUS activity was measured in transgenic plants. The results showed that PDULL1 was an endosperm-specific promoter. Further analysis showed that the promoter sequence (-343 to -1 base pairs) was sufficient for mediating GUS gene expression in endosperm. These results indicate that the region from -343 to -1 base pairs of PDULL1 is valuable for transgenic rice breeding and genetic engineering studies.

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Cloning and functional analysis of the promoter of a maize starch synthase III gene (ZmDULL1)

The invention relates to the technical fields of the molecular biology and the gene engineering, and concretely relates to a ZmWRKY58 gene obtained through the amplification in the total cDNA of a corn inbred line B73 by utilizing a PCR technology according to a transcription factor ZmWRKY58 gene sequence design primer. The gene codes a protein having one of amino acid residue sequences comprising SEQ ID No:1 in a sequence table, and an amino acid residue sequence obtained through substituting and/or deleting and/or adding 1-11 amino acid residues to the amino acid residue sequence represented by SEQ ID No:1 and having an interaction with a W box (TTGACC/T) cis-element to improve the stress resistances of plants. Results of onion cuticle subcell localization experiments show that the ZmWRKY58 protein has the nuclear localization characteristic of the transcription factor. The corn ZmWRKY58 gene is used for rice transformation, and obtained transgenic rice has an improved sensitivity to ABA, and has obviously-enhanced salt and drought tolerances. The corn ZmWRKY58 gene provides an important gene resource for the plant stress resistance gene engineering, and is of great significance to the improvement of the output of crops.

Corn WRKY transcription factor ZmWRKY58, and coding gene and application thereof

The invention discloses a corn endosperm tissue specificity promoter and application thereof, aiming at providing the corn endosperm tissue specificity promoter and application of the corn endosperm tissue specificity promoter to gene regulation, control and screening for expression in plants. The promoter has the following nucleotide sequences: (1) DNA sequence of SEQIDNO:1 in a sequence table; and (2), a nucleotide sequence capable of hybridizing with the DNA sequence defined by SEQIDNO:1 in the sequence table under a highly strict condition. The promoter can guide an exogenous gene to express in specific time and space during plant development, transgenic rice screened by the method has the advantages of strong stage characteristic and high sensitivity, as the screened gene only can be expressed in an endosperm stage and cannot be expressed in other periods, expression products of a target gene can be accumulated in certain space, region expression amount is increased, unnecessary waste of plant nutrients is avoided, the yield is improved, and high practical application value is achieved.

Cuiping Jiang

Papers

Genome-wide identification and characterization of maize expansin genes expressed in endosperm.

PIGD: a database for intronless genes in the Poaceae

Cloning and functional analysis of the promoter of a maize starch synthase III gene (ZmDULL1)

Corn WRKY transcription factor ZmWRKY58, and coding gene and application thereof

Corn endosperm tissue specificity promoter and application thereof