Expression patterns of three α-expansin isoforms in Coffea arabica during fruit development

Transcriptome and Anatomical Comparisons Reveal the Effects of Methyl Jasmonate on the Seed Development of Camellia oleifera

Seed is a major storage organ that determines the yield and quality of Camellia oleifera (C. oleifera). Methyl jasmonate (MeJA) is a signaling molecule involved in plant growth and development. However, the role of MeJA in the development of C. oleifera seeds remains a mystery. This study demonstrated that the larger seeds induced by MeJA resulted from more cell numbers and a larger cell area in the outer seed coat and embryo at the cellular level. At the molecular level, MeJA could regulate the expression of factors in the known signaling pathways of seed size control as well as cell proliferation and expansion, resulting in larger seeds. Furthermore, the accumulation of oil and unsaturated fatty acids due to MeJA-inducement was attributed to the increased expression of fatty acid biosynthesis-related genes but reduced expression of fatty acid degradation-related genes. CoMYC2, a key regulator in jasmonate signaling, was considered a potential hub regulator which directly interacted with three hub genes (CoCDKB2-3, CoCYCB2-3, and CoXTH9) related to the seed size and two hub genes (CoACC1 and CoFAD2-3) related to oil accumulation and fatty acid biosynthesis by binding to their promoters. These findings provide an excellent target for the improvement of the yield and quality in C. oleifera.

Regulation of α-expansins genes in Arabidopsis thaliana seeds during post-osmopriming germination

Seed osmopriming is a pre-sowing treatment that involves limitation of the seed water imbibition, so that pre-germinative metabolic activities proceed without radicular protrusion. This technique is used for improving germination rate, uniformity of seedling growth and hastening the time to start germination. In Arabidopsis thaliana, seed germination has been associated with the induction of enzymes involved in cell wall modifications, such as expansins. The α-expansins (EXPAs) are involved in cell wall relaxation and extension during seed germination. We used online tools to identify AtEXPA genes with preferential expression during seed germination and RT-qPCR to study the expression of five EXPA genes at different germination stages of non-primed and osmoprimed seeds. In silico promoter analysis of these genes showed that motifs similar to cis-acting elements related to abiotic stress, light and phytohormone responses are the most overrepresented in promoters of these AtEXPA genes, showing that their expression is likely be regulated by intrinsic developmental and environmental signals during Arabidopsis seed germination. The osmopriming conditioning had a decreased time and mean to 50% germination without affecting the percentage of final seed germination. The dried PEG-treated seeds showed noticeable high mRNA levels earlier at the beginning of water imbibition (18 h), showing that transcripts of all five EXPA isoforms were significantly produced during the osmopriming process. The strong up-regulation of these AtEXPA genes, mainly AtEXPA2, were associated with the earlier germination of the osmoprimed seeds, which qualifies them to monitor osmopriming procedures and the advancement of germination.

Expansin genes expression in growing ovaries and grains of sunflower are tissue-specific and associate with final grain weight

BACKGROUND

Grain weight (GW) is a key component of sunflower yield and quality, but may be limited by maternal tissues. Cell growth is influenced by expansin proteins that loosen the plant cell wall. This study aimed to identify spatio-temporal expression of EXPN genes in sunflower reproductive organ tissues (ovary, pericarp, and embryo) and evaluate correlations between reproductive organ growth and expansin genes expression. Evaluations involved eight different developmental stages, two genotypes, two source-sink treatments and two experiments. The genotypes evaluated are contrasting in GW (Alybro and confection variety RHA280) under two source-sink treatments (control and shaded) to study the interactions between grain growth and expansin genes expression.

RESULTS

Ovaries and grains were sampled at pre- and post-anthesis, respectively. Final GW differed between genotypes and shading treatments. Shading treatment decreased final GW by 16.4 and 19.5% in RHA280 and Alybro, respectively. Relative expression of eight expansin genes were evaluated in grain tissues. EXPN4 was the most abundant expansin in the ovary tissue, while EXPN10 and EXPN7 act predominantly in ovary and pericarp tissues, and EXPN1 and EXPN15 in the embryo tissues.

CONCLUSIONS

Specific expansin genes were expressed in ovary, pericarp and embryo in a tissue-specific manner. Differential expression among grain tissues was consistent between genotypes, source-sink treatments and experiments. The correlation analysis suggests that EXPN genes could be specifically involved in grain tissue extension, and their expression could be linked to grain size in sunflower.

Differentially Accumulated Proteins in Coffea arabica Seeds during Perisperm Tissue Development and Their Relationship to Coffee Grain Size

Coffee is one of the most important crops for developing countries. Coffee classification for trading is related to several factors, including grain size. Larger grains have higher market value then smaller ones. Coffee grain size is determined by the development of the perisperm, a transient tissue with a highly active metabolism, which is replaced by the endosperm during seed development. In this study, a proteomics approach was used to identify differentially accumulated proteins during perisperm development in two genotypes with regular (IPR59) and large grain sizes (IPR59-Graudo) in three developmental stages. Twenty-four spots were identified by MALDI-TOF/TOF-MS, corresponding to 15 proteins. We grouped them into categories as follows: storage (11S), methionine metabolism, cell division and elongation, metabolic processes (mainly redox), and energy. Our data enabled us to show that perisperm metabolism in IPR59 occurs at a higher rate than in IPR59-Graudo, which is supported by the accumulation of energy and detoxification-related proteins. We hypothesized that grain and fruit size divergences between the two coffee genotypes may be due to the comparatively earlier triggering of seed development processes in IPR59. We also demonstrated for the first time that the 11S protein is accumulated in the coffee perisperm.

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

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.

Salt stress alters the cell wall polysaccharides and anatomy of coffee (Coffea arabica L.) leaf cells

Coffea arabica is the most important agricultural commodity in the world, and salinity is a major threat to its sustainable irrigation. Coffee leaf polysaccharides from plants subjected to salt stress were extracted and the leaves visualized through optical and electron microscopy. Alterations were detected in the monosaccharide composition of the pectin and hemicelluloses, with increases in uronic acid in all fractions. Changes in the polysaccharides were confirmed by HPSEC and FTIR. Moreover, the monolignol content was increased in the final residue, which suggests increased lignin content. The cytoplasm was altered, and the chloroplasts appeared irregular in shape. The arrangement of the stroma lamellae was disordered, and no starch granules were present. It was concluded that leaves of C. arabica under salt stress showed alterations in cell wall polysaccharides, increased monolignol content and structural damage to the cells of the mesophyll.

AtEXP2 is involved in seed germination and abiotic stress response in Arabidopsis

Expansins are cell wall proteins that promote cell wall loosening by inducing pH-dependent cell wall extension and stress relaxation. Expansins are required in a series of physiological developmental processes in higher plants such as seed germination. Here we identified an Arabidopsis expansin gene AtEXPA2 that is exclusively expressed in germinating seeds and the mutant shows delayed germination, suggesting that AtEXP2 is involved in controlling seed germination. Exogenous GA application increased the expression level of AtEXP2 during seed germination, while ABA application had no effect on AtEXP2 expression. Furthermore, the analysis of DELLA mutants show that RGL1, RGL2, RGA, GAI are all involved in repressing AtEXP2 expression, and RGL1 plays the most dominant role in controlling AtEXP2 expression. In stress response, exp2 mutant shows higher sensitivity than wild type in seed germination, while overexpression lines of AtEXP2 are less sensitive to salt stress and osmotic stress, exhibiting enhanced tolerance to stress treatment. Collectively, our results suggest that AtEXP2 is involved in the GA-mediated seed germination and confers salt stress and osmotic stress tolerance in Arabidopsis.

A genome-wide analysis of the expansin genes in Malus × Domestica

Expansins were first identified as cell wall-loosening proteins; they are involved in regulating cell expansion, fruits softening and many other physiological processes. However, our knowledge about the expansin family members and their evolutionary relationships in fruit trees, such as apple, is limited. In this study, we identified 41 members of the expansin gene family in the genome of apple (Malus × Domestica L. Borkh). Phylogenetic analysis revealed that expansin genes in apple could be divided into four subfamilies according to their gene structures and protein motifs. By phylogenetic analysis of the expansins in five plants (Arabidopsis, rice, poplar, grape and apple), the expansins were divided into 17 subgroups. Our gene duplication analysis revealed that whole-genome and chromosomal-segment duplications contributed to the expansion of Mdexpansins. The microarray and expressed sequence tag (EST) data showed that 34 Mdexpansin genes could be divided into five groups by the EST analysis; they may also play different roles during fruit development. An expression model for MdEXPA16 and MdEXPA20 showed their potential role in developing fruit. Overall, our study provides useful data and novel insights into the functions and regulatory mechanisms of the expansin genes in apple, as well as their evolution and divergence. As the first step towards genome-wide analysis of the expansin genes in apple, our results have established a solid foundation for future studies on the function of the expansin genes in fruit development.

Callose and cellulose synthase gene expression analysis from the tight cluster to the full bloom stage and during early fruit development in Malus × domestica

Apple (Malus × domestica) is an economically important temperate fruit-bearing crop which belongs to the family of Rosaceae and its pomaceous fruit is one of the most commonly cultivated. Several studies have demonstrated that the cell wall plays a pivotal role during flower and fruit development. It takes active part in pollen tube growth and contributes to determine the fruit firmness trait through the action of cell wall-related enzymes (i.e. polygalacturonase and pectinmethylesterase). We have investigated the expression of callose and cellulose synthase genes during flowering from tight cluster to anthesis and during early fruit development in domesticated apple. We also link the changes observed in gene expression to the profile of soluble non-structural carbohydrates at different developmental stages of flowers/fruitlets and to the qualitative results linked to wall polysaccharides' composition obtained through near-infrared spectroscopy. This work represents an important addition to the study of tree physiology with respect to the analysis of the expression of callose and cellulose synthase genes during flower and early fruit development in domesticated apple.

Gene expression and enzymatic activity of pectin methylesterase during fruit development and ripening in Coffea arabica L

Coffee quality is directly related to the harvest and post harvest conditions. Non-uniform maturation of coffee fruits, combined with inadequate harvest, negatively affects the final quality of the product. Pectin methylesterase (PME) plays an important role in fruit softening due to the hydrolysis of methylester groups in cell wall pectins. In order to characterize the changes occurring during coffee fruit maturation, the enzymatic activity of PME was measured during different stages of fruit ripening. PME activity progressively increased from the beginning of the ripening process to the cherry fruit stage. In silico analysis of expressed sequence tags of the Brazilian Coffee Genome Project database identified 5 isoforms of PME. We isolated and cloned a cDNA homolog of PME for further characterization. CaPME4 transcription was analyzed in pericarp, perisperm, and endosperm tissues during fruit development and ripening as well as in other plant tissues. Northern blot analysis revealed increased transcription of CaPME4 in the pericarp 300 days after flowering. Low levels of CaPME4 mRNAs were observed in the endosperm 270 days after flowering. Expression of CaPME4 transcripts was strong in the branches and lower in root and flower tissues. We showed that CaPME4 acts specifically during the later stages of fruit ripening and possibly contributes to the softening of coffee fruit, thus playing a significant role in pectin degradation in the fruit pericarp.

Heat stress causes alterations in the cell-wall polymers and anatomy of coffee leaves (Coffea arabica L.)

Coffee plants were subjected to heat stress (37 °C) and compared with control plants (24 °C). Cell wall polysaccharides were extracted using water (W), EDTA (E) and 4M NaOH (H30 and H70). In addition, monolignols were analyzed, and the leaves were observed by microscopy. Plants under heat stress accumulated higher contents of arabinose and galactose in fraction W. Xylose contents were observed to decrease in H30 fractions after the heat stress, whereas galactose and uronic acid increased. H70 fractions from plants exposed to heat stress showed increased xylose contents, whereas the contents of arabinose and glucose decreased. Differences in the molar-mass profiles of polysaccharides were also observed. The primary monolignol contents increased after the heat stress. Structural alterations in palisade cells and ultrastructural damage in chloroplasts were also observed. Our results demonstrate that the chemical profile of coffee cell-wall polymers and structural cell anatomy change under heat stress.