Double mutants of granule-bound starch synthases, GBSSI and GBSSII, revealed their roles and the existence of amylose-like branched α-glucans in rice.

Double mutants of rice GBSS enzymes reveal amylose-like branched α-glucans are synthesized by other enzymes besides GBSSI and GBSSII.

• Why it matters: Understanding the specific roles of GBSSI and GBSSII in amylose synthesis is crucial for manipulating rice starch properties, but their exact functions and the presence of alternative pathways remain unclear.
• What they did: The study isolated rice gbss2 mutants and generated gbss1 gbss2 double mutants, then used iodine staining, gel filtration chromatography, and structural analyses to examine amylose and α-glucan synthesis in different organs.
• The result: Amylose in rice pollen is produced by GBSSI, while GBSSII synthesizes amylose in leaves and roots; however, amylose-like branched α-glucans persist in mutants, indicating other enzymes may synthesize these structures.