Wheat [Triticum aestivum L.] has two copies of Starch Synthase III gene, each encodes three homeologous proteins and exhibits genotype and tissue-specific expression under heat stress

Abstract

Starch synthase III is associated with starch accumulation in wheat. In-silico characterization indicated two homologous copies of TaSSIII gene, TaSSIIIa, and TaSSIIIb, on plus strand of chromosome 1 and minus strand of chromosome 2, respectively. TaSSIIIa shares maximum similarity with HvSSIIIa whereas, TaSSIIIb exhibited maximum similarity with OsSSIIIb. It encodes proteins with N-terminal transit peptide, SSIII-specific domain, C-terminal catalytic domain, and conserved glycosyl-transferase domain with variations among the homeologs. The catalytic domain has N-glycosylation motifs, PKC-Phospho motifs, CK2-Phospho motifs, and N-Myristyl motifs with different numbers in two homologs. ADP glucose binding motifs KVGGL and KTGGL are present in the N-terminal and C-terminal of the SS-CD and GT-1 domains, respectively. ITRLT and FEPCGLT ADP binding pockets are present at the C-terminus of catalytic domains. Maximum heterogen ligands are found in TaSSIIIa1B and minimum in the TaSSIIIb2B. TaSSIIIb expresses in leaf, stem, root, spike, & grain, and much higher amounts than TaSSIIIa. Pot-grown wheat genotypes showed heat stress induced up-regulation of the genes TaSSIIIa1D and TaSSIIIb2D in the flag leaf. 14.6-fold and 9.8-fold increase in the transcript level of TaSSIIIa1D and TaSSIIIb2D was observed in IC252874 (heat tolerant) under heat stress respectively, significantly higher than genotypes RAUWB-7, PBW 343, DBW 187, DH5 167, and HD 2967. Under the stress in field, transcript level change for TaSSIIIa1D was higher in the flag leaf and that of TaSSIIIb2D was higher in peduncle. The gene copies have tissue and genotype specific expression, get influenced by heat stress, and thus may have a role in homeostasis of starch synthesis.