In Planta Expression of Thermophilic GtGBE Mimics BEIIb and Modifies Rice Starch Structure Without Yield Penalties

Area of Science:

• Plant Biotechnology
• Biochemistry
• Food Science

Background:

• Enzymatic modification of starch using glycosyltransferases is a green approach to enhance starch functionality.
• Challenges include high enzyme production costs and inefficiency.
• Tailoring starch branching structures in planta offers a viable alternative.

Purpose of the Study:

• To develop an in planta strategy for modifying starch branching structures by heterologously expressing an α-glucan branching enzyme (GtGBE) in rice.
• To investigate promoter-dependent GtGBE expression effects on starch structure and properties.
• To assess the potential for agricultural and industrial applications.

Main Methods:

• Generated transgenic rice lines expressing GtGBE under endosperm-specific (pBEIIb) or constitutive (pUbi) promoters.
• Analyzed starch branching patterns, amylose content, crystallinity, and gelatinization properties.
• Evaluated GtGBE expression stability under heat stress and impact on agronomic traits.

Main Results:

• Promoter-dependent GtGBE expression modulated starch branching, reducing amylose and increasing short amylopectin chains.
• Modified starch exhibited decreased crystallinity, gelatinization temperatures, and viscosity, with improved retrogradation resistance.
• pBEIIb-driven GtGBE showed heat stability; pUbi-driven GtGBE enhanced grain weight and number without compromising agronomic traits.

Conclusions:

• Heterologous expression of GtGBE in rice is an effective molecular tool for direct, tailored bioengineering of starch in planta.
• This strategy offers dual potential for agricultural improvements and industrial starch applications.
• The approach addresses limitations of current enzymatic starch modification methods.