A genome-wide survey of glycolytic genes in diploid Asian cotton (Gossypium arboreum)

Molecular and biochemical characterization of the sunflower (Helianthus annuus L.) cytosolic and plastidial enolases in relation to seed development

In the present study, we describe the molecular and biochemical characterization of sunflower (Helianthus annuus L.) enolase (ENO, EC 4.2.1.11) proteins, which catalyze the formation of phosphoenolpyruvate, the penultimate intermediate in the glycolytic pathway. We cloned and characterized three cDNAs encoding different ENO isoforms from developing sunflower seeds. Studies using fluorescently tagged ENOs confirmed the predicted subcellular localization of ENO isoforms: HaENO1 in the plastid while HaENO2 and HaENO3 were found in the cytosol. The cDNAs were used to express the corresponding 6(His)-tagged proteins in Escherichia coli. The proteins were purified to electrophoretic homogeneity, using immobilized metal ion affinity chromatography, and biochemically characterized. Recombinant HaENO1 and HaENO2, but not HaENO3 were shown to have enolase activity, in agreement with data obtained with the Arabidopsis homolog proteins. Site directed mutagenesis of several critical amino acids was used to attempt to recover enolase activity in recombinant HaENO3, resulting in very small increases that were not additive. A kinetic characterization of the two active isoforms showed that pH had similar effect on their velocity, that they had similar affinity for 2-phosphoglycerate, but that the k_cat/K_m of the plastidial enzyme was higher than that of the cytosolic isoform. Even though HaENO2 was always the most highly expressed transcript, the levels of expression of the three ENO genes were remarkably distinct in all the vegetative and reproductive tissues studied. This indicates that in seeds the conversion of 2-phosphoglycerate to phosphoenolpyruvate takes place through the cytosolic and the plastidial pathways therefore both routes could contribute to the supply of carbon for lipid synthesis. The identity of the main source of carbon during the period of stored products synthesis is discussed.

Genome-wide identification and characterization of phospholipase C gene family in cotton (Gossypium spp.)

Phospholipase C (PLC) are important regulatory enzymes involved in several lipid and Ca²⁺-dependent signaling pathways. Previous studies have elucidated the versatile roles of PLC genes in growth, development and stress responses of many plants, however, the systematic analyses of PLC genes in the important fiber-producing plant, cotton, are still deficient. In this study, through genome-wide survey, we identified twelve phosphatidylinositol-specific PLC (PI-PLC) and nine non-specific PLC (NPC) genes in the allotetraploid upland cotton Gossypium hirsutum and nine PI-PLC and six NPC genes in two diploid cotton G. arboretum and G.raimondii, respectively. The PI-PLC and NPC genes of G. hirsutum showed close phylogenetic relationship with their homologous genes in the diploid cottons and Arabidopsis. Segmental and tandem duplication contributed greatly to the formation of the gene family. Expression profiling indicated that few of the PLC genes are constitutely expressed, whereas most of the PLC genes are preferentially expressed in specific tissues and abiotic stress conditions. Promoter analyses further implied that the expression of these PLC genes might be regulated by MYB transcription factors and different phytohormones. These results not only suggest an important role of phospholipase C members in cotton plant development and abiotic stress response but also provide good candidate targets for future molecular breeding of superior cotton cultivars.

Cotton cytosolic pyruvate kinase GhPK6 participates in fast fiber elongation regulation in a ROS-mediated manner

Cotton cytosolic pyruvate kinase GhPK6 is preferentially expressed in the late stage of fiber elongation process, transgenic experiments indicated that its expression level was negatively correlated to cell expansion rate. Pyruvate kinase (PK) plays vital regulatory roles in rapid cell growth in mammals. However, the function of PK in plant cell growth remains unclear. In allotetraploid upland cotton (Gossypium hirsutum L.), a total of 33 PK genes are encoded by the genome. Analysis of the transcriptome data indicated that only two cytosolic PK genes, GhPK6 and its duplicated gene GhPK26, are preferentially expressed in elongating cotton fiber cells. RT-qPCR and western blot analyses revealed that the expression of GhPK6 was negatively correlated with fiber elongation rate, which well explains the observed sharp increase of cytosolic PK activity at the end of fast fiber elongation process. Furthermore, virus-induced gene silencing of GhPK6 in cotton plants resulted in increased fiber cell elongation and reduced reactive oxygen species (ROS) accumulation. On the contrary, Arabidopsis plants ectopically expressing GhPK6 exhibited ROS-mediated growth inhibition, whereas the addition of ROS scavenging reagents could partly rescue this inhibition. These data collectively suggested that GhPK6 might play an important role in regulating cotton fiber elongation in a ROS-dependent inhibition manner.