ThePsychedelicGenes of Maize Redundantly Promote Carbohydrate Export From Leaves

Abstract

Whole-plant carbohydrate partitioning involves the assimilation of carbon in leaves and its translocation to nonphotosynthetic tissues. This process is fundamental to plant growth and development, but its regulation is poorly understood. To identify genes controlling carbohydrate partitioning, we isolated mutants that are defective in exporting fixed carbon from leaves. Here we describe psychedelic (psc), a new mutant of maize (Zea mays) that is perturbed in carbohydrate partitioning. psc mutants exhibit stable, discrete chlorotic and green regions within their leaves. psc chlorotic tissues hyperaccumulate starch and soluble sugars, while psc green tissues appear comparable to wild-type leaves. The psc chlorotic and green tissue boundaries are usually delineated by larger veins, suggesting that translocation of a mobile compound through the veins may influence the tissue phenotype. psc mutants display altered biomass partitioning, which is consistent with reduced carbohydrate export from leaves to developing tissues. We determined that the psc mutation is unlinked to previously characterized maize leaf carbohydrate hyperaccumulation mutants. Additionally, we found that the psc mutant phenotype is inherited as a recessive, duplicate-factor trait in some inbred lines. Genetic analyses with other maize mutants with variegated leaves and impaired carbohydrate partitioning suggest that Psc defines an independent pathway. Therefore, investigations into the psc mutation have uncovered two previously unknown genes that redundantly function to regulate carbohydrate partitioning in maize.

Tie-dyed2Encodes a Callose Synthase That Functions in Vein Development and Affects Symplastic Trafficking within the Phloem of Maize Leaves

“…PCR using Mu-and gene-specific primers was used to genotype tdy2-Mu mutant plants (Supplemental Table S1). Plants were grown as reported previously (Braun et al, 2006;Huang et al, 2009;Slewinski and Braun, 2010b). The tdy2-R mutant was used for the analyses.…”

“…Epidermal nail-polish impressions (Reynolds et al, 1998), callose and starch staining (Braun et al, 2006;Baker and Braun, 2008;Slewinski and Braun, 2010b), and TEM were performed as described. For TEM, four minor veins (three small, one intermediate) that function in Suc phloem loading were harvested from a fully expanded adult leaf and examined in serial sections until a total of 100 individual vascular bundle sections were examined per leaf sample (n = 3, corresponding to 12 minor veins) for wildtype and tdy2 yellow leaf tissues, respectively.…”

“…Genetic screens for mutants that hyperaccumulate carbohydrates in their leaves could be used to identify genes functioning in any of the above steps, including Suc export from the phloem, symplastic transport, starch catabolism in the photosynthetic cells, and phloem development (Russin et al, 1996;Blauth et al, 2001;Dinges et al, 2003;Braun et al, 2006;Baker and Braun, 2008;Slewinski et al, 2009;Slewinski and Braun, 2010b). In maize, loss-of-function mutations in the Sut1 gene confer a strong carbohydrate hyperaccumulation phenotype in leaves (Slewinski et al, , 2010.…”

Maize SUT1 functions in phloem loading

“…[13][14][15] mutants. [16][17][18][19][20][21][22][23][24][25] Guttation fluid was collected from untreated wild-type sibling and sut1-m1 mutant plants and assayed for soluble sugar concentrations. Wildtype guttation fluid contained very low sugar concentrations, whereas guttation fluid from sut1-m1 leaves contained over 700 mg of sucrose/g of fluid and 20-25 mg each of glucose and fructose/g of fluid ( Fig.…”

Tonoplast Sugar Transporters (SbTSTs) putatively control sucrose accumulation in sweet sorghum stems

“…Hence, characterizing the genes that function in sucrose transport and storage will reveal potential new targets for future manipulations to enhance crop yields. 3,4,[12][13][14][15][16] Different sorghum genotypes have been selectively bred to store carbohydrates in contrasting storage organs: sweet sorghums accumulate large quantities of soluble sugars, mostly sucrose, in stem tissues, whereas grain sorghums primarily store carbohydrates as starch in the seeds. 1,2,6,17,18 The molecular basis for the difference in carbohydrate partitioning between these sorghum types is unknown.…”