A Dual-Promoter Gene Orchestrates the Sucrose-Coordinated Synthesis of Starch and Fructan in Barley

Abstract

Sequential carbohydrate synthesis is important for plant survival because it guarantees energy supplies for growth and development during plant ontogeny and reproduction. Starch and fructan are two important carbohydrates in many flowering plants and in human diets. Understanding this coordinated starch and fructan synthesis and unraveling how plants allocate photosynthates and prioritize different carbohydrate synthesis for survival could lead to improvements to cereals in agriculture for the purposes of greater food security and production quality. Here, we report a system from a single gene in barley employing two alternative promoters, one intronic/exonic, to generate two sequence-overlapping but functionally opposing transcription factors, in sensing sucrose, potentially via sucrose/glucose/fructose/trehalose 6-phosphate signaling. The system employs an autoregulatory mechanism in perceiving a sucrose-controlled trans activity on one promoter and orchestrating the coordinated starch and fructan synthesis by competitive transcription factor binding on the other promoter. As a case in point for the physiological roles of the system, we have demonstrated that this multitasking system can be exploited in breeding barley with tailored amounts of fructan to produce healthy food ingredients. The identification of an intron/exon-spanning promoter in a hosting gene, resulting in proteins with distinct functions, adds to the complexity of plant genomes.

Adaptation of Rice to the Nordic Climate Yields Potential for Rice Cultivation at Most Northerly Site and the Organic Production of Low-Arsenic and High-Protein Rice

“…Biological and technical triplicates were used in all experiments except analysis of starch and amylose in which technical duplicates were used according to the manufacturer's protocols (Megazyme, Bray, Co. Wicklow, Ireland). One-way ANOVA was used for analysis as described previously (Jin et al, 2017a).…”

“…Rice grains were grounded and dried completely. The starch and amylose content were analyzed by Megazyme kits for total starch and amylose/amylopectin, respectively (Megazyme, Bray, Co. Wicklow, Ireland), and as described in Jin et al (2017a) and Sun et al (2005).…”

The Sugar-Signaling Hub: Overview of Regulators and Interaction with the Hormonal and Metabolic Network

“…In agreement with this, SUSIBA2-expressing rice preferentially reallocates photosynthates towards aboveground tissues (stem and seeds); this offers sustainable means of increasing starch contents for food production and limits root-related greenhouse gas emission during rice cultivation [ 127 ]. In barley leaves, SUSIBA1 and SUSIBA2 are involved in an antagonistic SUSIBA regulatory network that ultimately leads to the coordination of starch and fructan synthesis in response to sugar availability [ 128 ]. Low sucrose concentrations generally upregulate SUSIBA1 expression, which acts as a repressor of both fructan synthesis and SUSIBA2 expression, while high sucrose levels induce SUSIBA2 expression, which stimulates starch accumulation in leaves but represses SUSIBA1 expression.…”

“…Low sucrose concentrations generally upregulate SUSIBA1 expression, which acts as a repressor of both fructan synthesis and SUSIBA2 expression, while high sucrose levels induce SUSIBA2 expression, which stimulates starch accumulation in leaves but represses SUSIBA1 expression. This intertwined regulation shows that SUSIBA2 expression depends on the competitive binding of SUSIBA1 (repressor)/SUSIBA2 (inducer) to the target site (W-box) of the SUSIBA2 promoter, building up an autoregulatory system for the sequential regulation of starch and fructan synthesis [ 128 ]. Noteworthy, we do not know as yet whether the SUSIBA-related function in sugar signaling is evolutionarily conserved in eudicots.…”

Mechanism of Allium Crops Bulb Enlargement in Response to Photoperiod: A Review

“…Therefore, it is likely that the variation of bulb at the suitable time in diverse latitudes comprises similar mechanisms. Leek is a significant Allium crop that does not contain bulbs and consequently privations a photoperiodic obligation [229][230][231][232][233][234][235]. These landscapes let leeks be implanted during the whole season and fully grow over a wide range of latitudes.…”