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Starch deposited in the endosperm of cereal seeds serves as a source of food and animal feed, and as a substrate for bioethanol production. To gain insights into the molecular mechanisms underlying genetic variation in seed size and seed starch content, this study investigated transcriptional regulation of starch biosynthesis genes during seed filling in two wheat genotypes that exhibit contrasting phenotype in seed size. Our data showed that variation in starch accumulation during seed filling is closely associated with modulations in the expression patterns of specific starch biosynthesis genes including TaAGPL1, TaAGPS2, TaGBSSI, TaSSI, TaSSIV, TaSBEIIa, TaISA1, and TaISA3, as well as alterations in the activity of AGPase, GBSS, and SS enzymes. Consistently, the genotype that produces larger seeds that are characterized by a higher seed starch content generated higher amounts of fermentable sugars and bioethanol before and after fermentation, respectively. Since the amount of phenol per seed dry weight is higher in the genotype that produces smaller seeds, the prevalence of lower starch to bioethanol conversion efficiency in this genotype, despite the higher amount of glucose generated per bioavailable starch, suggests that the phenolic compounds interfere with the fermentation process and thereby affecting the bioethanol yield. [ABSTRACT FROM AUTHOR]

To gain insights into the molecular mechanisms underlying hormonal regulation in adventitious roots and during their emergence under waterlogged conditions in wheat, the present study investigated transcriptional regulation of genes related to hormone metabolism and transport in the root and stem node tissues. Waterlogging-induced inhibition of axile root elongation and lateral root formation, and promotion of surface adventitious and axile root emergence and aerenchyma formation are associated with enhanced expression levels of ethylene biosynthesis genes, ACS7 and ACO2 , in both tissues. Inhibition of axile root elongation is also related to increased root indole acetic acid (IAA) and jasmonate (JA) levels that are associated with up-regulation of specific IAA biosynthesis/transport (TDC , YUC1 , and PIN9) and JA metabolism (LOX8 , AOS1 , AOC1 , and JAR1) genes, and transcriptional alteration of gibberellin (GA) metabolism genes (GA3ox2 and GA2ox8). Adventitious root emergence from waterlogged stem nodes is associated with increased levels of IAA and GA but decreased levels of cytokinin and abscisic acid (ABA), which are regulated through the expression of specific IAA biosynthesis/transport (TDC , YUC1 , and PIN9), cytokinin metabolism (IPT5-2 , LOG1 , CKX5 , and ZOG2), ABA biosynthesis (NCED1 and NCED2), and GA metabolism (GA3ox2 and GA2ox8) genes. These results enhance our understanding of the molecular mechanisms underlying the adaptive response of wheat to waterlogging. [ABSTRACT FROM AUTHOR]

Background Sucrose transporters (SUTs) play important roles in regulating the translocation of assimilates from source to sink tissues. Identification and characterization of new SUTs in economically important crops such as wheat provide insights into their role in determining seed yield. To date, however, only one SUT of wheat has been reported and functionally characterized. The present study reports the isolation and characterization of a new SUT, designated as TaSUT2, and its homeologues (TaSUT2A, TaSUT2B and TaSUT2D) in hexaploid wheat (Triticum aestivum L.). Results TaSUT2A and TaSUT2B genes each encode a protein with 506 amino acids, whereas TaSUT2D encodes a protein of 508 amino acids. The molecular mass of these proteins is predicted to be ~ 54 kDA. Topological analysis of the amino acid sequences of the three homeologues revealed that they contain 12 transmembrane spanning helices, which are described as distinct characteristic features of glycoside-pentoside-hexuronide cation symporter family that includes all known plant SUTs, and a histidine residue that appears to be localized at and associated conformationally with the sucrose binding site. Yeast SUSY7/ura3 strain cells transformed with TaSUT2A, TaSUT2B and TaSUT2D were able to uptake sucrose and grow on a medium containing sucrose as a sole source of carbon; however, our subcellular localization study with plant cells revealed that TaSUT2 is localized to the tonoplast. The expression of TaSUT2 was detected in the source, including flag leaf blade, flag leaf sheath, peduncle, glumes, palea and lemma, and sink (seed) tissues. The relative contributions of the three genomes of wheat to the total expression of TaSUT2 appear to differ with tissues and developmental stages. At the cellular level, TaSUT2 is expressed mainly in the vein of developing seeds and subepidermal mesophyll cells of the leaf blade. Conclusion This study demonstrated that TaSUT2 is a new wheat SUT protein. Given that TaSUT2 is localized to the tonoplast and sucrose is temporarily stored in the vacuoles of both source and sink tissues, our data imply that TaSUT2 is involved in the intracellular partitioning of sucrose, particularly between the vacuole and cytoplasm. [ABSTRACT FROM AUTHOR]