Improving Agricultural Traits While Maintaining High Resistant Starch Content in Rice.

Area of Science:

• Plant genetics and breeding
• Food science and technology
• Biochemistry of carbohydrates

Background:

• Resistant starch (RS) offers health benefits, with loss of starch branching enzyme IIb (BEIIb) increasing RS content by promoting longer amylopectin chains.
• Elevated RS content in cereals often leads to reduced seed weight and undesirable agronomic traits, necessitating further genetic improvement.
• Introduction of active-type starch synthase (SS) IIa and high expression-type granule-bound SSI (GBSSI) genes into be2b mutant rice increased RS but required agricultural trait enhancement.

Purpose of the Study:

• To improve the agricultural traits of high resistant starch (RS) rice lines through backcrossing with an elite cultivar.
• To analyze the starch properties and RS content of the resultant high-yielding RS rice lines after backcrossing.
• To assess the impact of backcrossing on seed weight and other agronomic characteristics while maintaining high RS levels.

Main Methods:

• High RS rice lines, engineered with genes for increased RS content, were subjected to multiple generations of backcrossing with an elite rice cultivar.
• Agronomic traits, including seed weight, flowering time, and grain characteristics, were evaluated in the backcrossed lines.
• Starch properties, such as amylopectin structure, gelatinization temperature, and RS content, were analyzed using biochemical methods.

Main Results:

• Backcrossing significantly improved seed weight by up to 190% compared to pre-backcrossed high RS lines, without altering amylopectin structure or RS content.
• High RS lines exhibited longer amylopectin branch chains, with active-type SSIIa contributing to higher gelatinization temperatures.
• Cooked rice from high RS lines consistently showed high RS content (27-35%), significantly higher than the elite parent ( < 0.7%).

Conclusions:

• Backcrossing high RS rice lines with elite cultivars effectively enhances seed weight and improves agronomic traits without compromising RS content.
• The process likely introduced beneficial loci for seed size and flowering time, optimizing conditions for RS biosynthesis.
• This strategy offers a viable approach to developing high-yielding rice varieties with enhanced nutritional value due to high RS content.