Integument-Specific Transcriptional Regulation in the Mid-Stage of Flax Seed Development Influences the Release of Mucilage and the Seed Oil Content

Flax (Linum usitatissimum L.) seed oil, which accumulates in the embryo, and mucilage, which is synthesized in the seed coat, are of great economic importance for food, pharmaceutical as well as chemical industries. Theories on the link between oil and mucilage production in seeds consist in the spatio-temporal competition of both compounds for photosynthates during the very early stages of seed development. In this study, we demonstrate a positive relationship between seed oil production and seed coat mucilage extrusion in the agronomic model, flax. Three recombinant inbred lines were selected for low, medium and high mucilage and seed oil contents. Metabolite and transcript profiling (1H NMR and DNA oligo-microarrays) was performed on the seeds during seed development. These analyses showed main changes in the seed coat transcriptome during the mid-phase of seed development (25 Days Post-Anthesis), once the mucilage biosynthesis and modification processes are thought to be finished. These transcriptome changes comprised genes that are putatively involved in mucilage chemical modification and oil synthesis, as well as gibberellic acid (GA) metabolism. The results of this integrative biology approach suggest that transcriptional regulations of seed oil and fatty acid (FA) metabolism could occur in the seed coat during the mid-stage of seed development, once the seed coat carbon supplies have been used for mucilage biosynthesis and mechanochemical properties of the mucilage secretory cells.

INTEGUMENT-SPECIFIC TRANSCRIPTIONAL REGULATION IN THE MID-STAGE OF FLAX SEED DEVELOPMENT INFLUENCES THE RELEASE OF MUCILAGE AND THE SEED OIL CONTENT

ABSTRACTFlax (Linum usitatissimum L.) seed oil, which accumulates in the embryo, and mucilage, which is synthesized in the seed coat, are of great economic importance for food, pharmaceutical as well as chemical industries. Theories on the link between oil and mucilage production in seeds consist in the spatio-temporal competition of both compounds for photosynthates during the very early stages of seed development. In this study, we demonstrate a positive relationship between seed oil production and seed coat mucilage extrusion in the agronomic model, flax. Three recombinant inbred lines were selected for low, medium and high mucilage and seed oil contents. Metabolite and transcript profiling (1H NMR and DNA oligo-microarrays) was performed on the seeds during seed development. These analyses showed main changes in the seed coat transcriptome during the mid-phase of seed development (25 Days Post-Anthesis), once the mucilage biosynthesis and modification processes are thought to be finished. These transcriptome changes comprised genes that are putatively involved in mucilage chemical modification and oil synthesis, as well as gibberellic acid (GA) metabolism. The results of these integrative biology approach, suggest that transcriptional regulations of seed oil and fatty acid (FA) metabolism could occur in the seed coat during the mid-stage of seed development, once the seed coat carbon supplies have been used for mucilage biosynthesis and mechanochemical properties of the mucilage secretory cells.

Isolation and Evaluation of Tamarind Seed Coat Mucilage as Pharmaceutical Suspending Agent

Natural polymers, specifical mucilages, have been used as a suspending agent for a long period of time. Natural excipients can serve as an alternative to synthetic products since they are less expensive, less toxic, and devoid of environmental pollution. The present study was undertaken to evaluate the mucilage isolated from Tamarindusindica (Fabaceae) seed coat, commonly named tamarind, as an innovative suspending agent. Paracetamol suspensions (10% w/v) were prepared using the T. indica seed coat mucilage as a suspending agent, and it was evaluated for parameters like physical stability, sedimentation profile, dispersibility, and flow property. Furthermore, it was assessed for its stability. The effect of the tested mucilage on the suspension was compared with commonly used suspending agents, i.e. sodium carboxymethyl cellulose (CMC) at concentrations of 0.5, 1.0, and 1.5% w/v. The results obtained indicated that the T. indica seed coat mucilage could be used as a suspending agent.

KNAT7 regulates xylan biosynthesis in Arabidopsis seed-coat mucilage

As a major hemicellulose component of plant cell walls, xylans play a determining role in maintaining the wall structure. However, the mechanisms of transcriptional regulation of xylan biosynthesis remain largely unknown. Arabidopsis seed mucilage represents an ideal system for studying polysaccharide biosynthesis and modifications of plant cell walls. Here, we identify KNOTTED ARABIDOPSIS THALIANA 7 (KNAT7) as a positive transcriptional regulator of xylan biosynthesis in seed mucilage. The xylan content was significantly reduced in the mucilage of the knat7-3 mutant and this was accompanied by significantly reduced expression of the xylan biosynthesis-related genes IRREGULAR XYLEM 14 (IRX14) and MUCILAGE MODIFIED 5/MUCILAGE-RELATED 21 (MUM5/MUCI21). Electrophoretic mobility shift assays, yeast one-hybrid assays, and chromatin immunoprecipitation with quantitative PCR verified the direct binding of KNAT7 to the KNOTTED1 (KN1) binding site [KBS,TGACAG(G/C)T] in the promoters of IRX7, IRX14, and MUM5/MUCI21 in vitro, in vivo, and in planta. Furthermore, KNAT7 directly activated the expression of IRX14 and MUM5/MUCI21 in transactivation assays in mesophyll protoplasts, and overexpression of IRX14 or MUM5/MUCI21 in knat7-3 partially rescued the defects in mucilage adherence. Taken together, our results indicate that KNAT7 positively regulates xylan biosynthesis in seed-coat mucilage via direct activation of the expression of IRX14 and MUM5/MUCI21.

Arabidopsis ERF4 and MYB52 Transcription Factors Play Antagonistic Roles in Regulating Homogalacturonan De-methylesterification in Seed Coat Mucilage

ABSTRACTThe Arabidopsis (Arabidopsis thaliana) seed coat mucilage is a specialized cell wall with pectin as its major component. Pectin is synthesized in the Golgi apparatus with homogalacturonan fully methylesterified, but it must undergo de-methylesterification by pectin methylesterase (PME) after being secreted into the cell wall. This reaction is critical for pectin maturation, but the mechanisms of its transcriptional regulation remain largely unknown. Here, we show that the Arabidopsis ERF4 transcription factor positively regulates pectin de-methylesterification during seed development and directly suppresses the expression of PME INHIBITOR13 (PMEI13), 14, 15 and SUBTILISIN-LIKE SERINE PROTEASE 1.7 (SBT1.7). The erf4 mutant seeds showed repartitioning of mucilage between soluble and adherent layers as a result of decreased PME activity and increased degree of pectin methylesterification. ERF4 physically associates with and antagonizes MYB52 in activating PMEI6, 14 and SBT1.7 and MYB52 also antagonizes ERF4 activity in the regulation of downstream targets. Gene expression studies revealed that ERF4 and MYB52 have opposite effects on pectin de-methylesterification. Genetic analysis indicated that the erf4-2 myb52 double mutant seeds show mucilage phenotype similar to wild-type. Taken together, this study demonstrates that ERF4 and MYB52 antagonize each other’s activity to maintain the appropriate degree of pectin methylesterification, expanding our understanding of how pectin de-methylesterification is fine-tuned by the ERF4-MYB52 transcriptional complex in the seed mucilage.One-sentence summaryArabidopsis ERF4 and MYB52 transcription factors interact and play antagonistic roles in regulating homogalacturonan de-methylesterification related genes in the seed coat mucilage.