ANKUMAH, N.

AVIGNE, W. T.

HUNTER, C. T.

KOCH, K. E.

SOUSA, S. M.

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P27The sdhl mutant alters kernel sugar composition and transcript profiles inaddition to its small-kernel phenotype.(submitted by Sylvia de Sousa <smsousa@ufl.edu»Full Author List: de Sousa, Sylvia M12; Hunter Ill, Charles TI; Ankumah, Nana': Avigne, Wayne TI;Koch, Karen E1I University ofFlorida, Gainesville, FL - USA - Fifield Hall- POBox 1106902 EMBRAPA Maize and Sorghum, Sete Lagoas, MG - BraziI- CP 285Sorbitol dehydrogenase (SDH) in maize kemels could mediate a centrally-positioned, second-step inmetabolism ofimported sucrose; that fructose use (fructose + NADH <-> sorbitol + NAD). This issignificant because fructose is produced regardless ofhow sucrose is cleaved (via invertase or sucrosesynthase), and sorbitol dehydrogenase provides a potentially advantageous altemative to other paths offructose use and sensing. To help test hypotheses for the significance of SDH in maize, we identified ansdhl mutant, as noted earlier, by screening the UniformMu maize population. The sdhl mutation reducedmaximal SDH activity in developing kemels to less than 6% of wild- type levels. The resulting phenotypewas a 21% smaller kemel under field conditions (dried-seed weight at maturity, significant to p<.OOl). Inthe present work, a 3'-UTR profiling strategy was used to generate gene-specific, sequence-basedexpression profiles for tissues ofwild-type and sdhl kemels. These tissues included pedicel + transferregion, embryo, embryo proximal region, peripheral endosperm, and pericarp. The 454-transcript profilesidentified altered expression of genes for specific metabolic pathways between regions within kemels, andbetween these zones in wild-type and sdh 1 mutants. A decrease was observed in the expression of thegenes involved in the putative sorbitol pathway. Metabolic analyses also showed that the sdhl mutationincreased sugar levels during development; especially at 25 DAP (near harvest date for many sweet coms).At this stage, hexose levels were more than doubled and sucrose levels were elevated by 16%. The sdhlmutation may thus have potential value for sweet com improvement. The 2-fold hexose increases alsoindicated a central role for sorbitol metabolism in the sugar balance of developing maize kemels. Thesechanges were accompanied by 33% reduction in sorbitollevels, but other paths of sorbitol biosynthesisappear likely in kemels, given the presence of significant residual sorbitol in the sdh 1mutant. ln addition,sdh 1 decreased mannose levels in the kemel, and levels of arabinose and xylose in the pericarp. The starchcontent was decreased in the kemel, but no difference was observed in the protein content. These resultsdemonstrate multiple effects of sdhl mutation in the maize kemel and importance of the sorbitol pathawayin metabolic and physical flux of carbon in developing maize kemels.P28Transcriptional profiling of Aspergillus flavus infected maize kernels.(submitted by Andrea Dolezal <aldoleza@ncsu.edu»Full Author List: Dolezal, Andrea L I; Boston, Rebecca SI; Payne, Gary A II North Carolina State University, Raleigh, NC, 27695, United States of America,Maize kemels are susceptible to infection by the opportunistic pathogen Aspergillusflavus. Infection results in areduction of grain quality and contamination of kemels with the highly carcinogenic mycotoxin, atlatoxin. To gain abetter understanding of the host response to infection by the fungus, transcription of approximately 9,000 maize geneswere monitored during the host-pathogen interaction. RNA was extracted 4 days after infection ofkemels at thedevelopmental stages ofblister, milk, dough,and dent, and hybridized to custom made Affymetrix GeneChip DNAmicroarrays. Analysis ofthese microarrays revealed a complex transcriptional response by maize to infection.Responses included the up regulation of over 1,000 maize genes with a fold change of two or greater. lncluded in thisresponse was increased expression of genes coding for proteins characteristic of plant defense such as, but not limited .to, Pathogenesis-related (PR) proteins, a xylenase inhibitor, and ethylene biosynthetic enzymcs. In addition, othertranscripts of interest found differentially expressed in the interaction were those associated with the basal endospermtransfer layer, BETL-4 and the cell wall invertase miniature seed I. Additional experiments are being performed usinga beta-glucuronidase- expressing A. flavus strain, as well as, histological stains to visualize fungal colonization withinthe kemel. Combined, these data give insight into maize defense mechanisms used against the opportunistic pathogenA. flavus and may lead to the development of control strategies for this disease.54

The SDH1 mutant alters kernel sugar composition and transcript profiles in addition to its small-kernel phenotype.

http://www.alice.cnptia.embrapa.br/alice/bitstream/doc/630782/1/SDH1mutant.pdf

The SDH1 mutant alters kernel sugar composition and transcript profiles in addition to its small-kernel phenotype.

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