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Divisions of labor in the thiamin biosynthetic pathway among organs of maize.

Guan JC, Hasnain G, Garrett TJ, Chase CD, Gregory J, Hanson AD, McCarty DR - Front Plant Sci (2014)

Bottom Line: By contrast, divergent patterns of THIC and THI4 expression occur in the shoot apical meristem, embyro sac, embryo, endosperm, and root-tips suggesting that these sink organs acquire significant amounts of thiamin via salvage pathways.Finally, stable isotope labeling experiments set an upper limit on the rate of de novo thiamin biosynthesis in maize leaf explants.Overall, the observed patterns of thiamin biosynthetic gene expression mirror the strategies for thiamin acquisition that have evolved in bacteria.

View Article: PubMed Central - PubMed

Affiliation: Genetics Institute and Horticultural Sciences Department, Institute of Food and Agricultural Sciences, University of Florida Gainesville, FL, USA.

ABSTRACT
The B vitamin thiamin is essential for central metabolism in all cellular organisms including plants. While plants synthesize thiamin de novo, organs vary widely in their capacities for thiamin synthesis. We use a transcriptomics approach to appraise the distribution of de novo synthesis and thiamin salvage pathways among organs of maize. We identify at least six developmental contexts in which metabolically active, non-photosynthetic organs exhibit low expression of one or both branches of the de novo thiamin biosynthetic pathway indicating a dependence on inter-cellular transport of thiamin and/or thiamin precursors. Neither the thiazole (THI4) nor pyrimidine (THIC) branches of the pathway are expressed in developing pollen implying a dependence on import of thiamin from surrounding floral and inflorescence organs. Consistent with that hypothesis, organs of the male inflorescence and flowers are shown to have high relative expression of the thiamin biosynthetic pathway and comparatively high thiamin contents. By contrast, divergent patterns of THIC and THI4 expression occur in the shoot apical meristem, embyro sac, embryo, endosperm, and root-tips suggesting that these sink organs acquire significant amounts of thiamin via salvage pathways. In the root and shoot meristems, expression of THIC in the absence of THI4 indicates a capacity for thiamin synthesis via salvage of thiazole, whereas the opposite pattern obtains in embryo and endosperm implying that seed storage organs are poised for pyrimidine salvage. Finally, stable isotope labeling experiments set an upper limit on the rate of de novo thiamin biosynthesis in maize leaf explants. Overall, the observed patterns of thiamin biosynthetic gene expression mirror the strategies for thiamin acquisition that have evolved in bacteria.

No MeSH data available.


Related in: MedlinePlus

Low expression of the thiamine biosynthetic pathway in developing pollen contrasts with high expression in surrounding floral organs. (A) Structure of the male inflorescence of maize (image, J. Saunders; art, K. E. Koch). (B) Gene expression in floral organs and developing pollen. RNA was quantified by qRT-PCR (see Methods). Late-binucleate stage pollen was isolated from developmentally staged anthers as described by Wen and Chase (1999). The Wx1 starch synthase was measured as a positive control for pollen gene expression. Error bars are standard error of the mean, n = 3.
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Figure 5: Low expression of the thiamine biosynthetic pathway in developing pollen contrasts with high expression in surrounding floral organs. (A) Structure of the male inflorescence of maize (image, J. Saunders; art, K. E. Koch). (B) Gene expression in floral organs and developing pollen. RNA was quantified by qRT-PCR (see Methods). Late-binucleate stage pollen was isolated from developmentally staged anthers as described by Wen and Chase (1999). The Wx1 starch synthase was measured as a positive control for pollen gene expression. Error bars are standard error of the mean, n = 3.

Mentions: To determine whether thiamin biosynthetic genes are expressed in developing pollen, we analyzed thiamin gene expression in pollen grains isolated during the starch-filling stage of pollen development. Figure 5 shows quantification of Thi1, Thi2 and THIC expression in the organs of the male inflorescence (Figure 5A); in binucleate-stage developing pollen; and in pre-anthesis stage anthers. The qRT-PCR results confirmed that expression of thiazole and pyrimidine biosynthetic genes is very low in both anthers and developing pollen in contrast to the high expression observed in rachis (stem of the male inflorescence) and rachilla and glume organs of the male flower. As a positive control, we assayed expression of Wx1, which is known to function in developing pollen (Nelson, 1962). As expected, developing anthers and pollen exhibited high relative expression of Wx1 supporting our conjecture that the starch biosynthetic pathway is down-regulated during pollen maturation most likely immediately prior to anthesis. By contrast, the de novo thiamin biosynthetic pathway is inactive in starch-filling pollen as well as mature pollen.


Divisions of labor in the thiamin biosynthetic pathway among organs of maize.

Guan JC, Hasnain G, Garrett TJ, Chase CD, Gregory J, Hanson AD, McCarty DR - Front Plant Sci (2014)

Low expression of the thiamine biosynthetic pathway in developing pollen contrasts with high expression in surrounding floral organs. (A) Structure of the male inflorescence of maize (image, J. Saunders; art, K. E. Koch). (B) Gene expression in floral organs and developing pollen. RNA was quantified by qRT-PCR (see Methods). Late-binucleate stage pollen was isolated from developmentally staged anthers as described by Wen and Chase (1999). The Wx1 starch synthase was measured as a positive control for pollen gene expression. Error bars are standard error of the mean, n = 3.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4120688&req=5

Figure 5: Low expression of the thiamine biosynthetic pathway in developing pollen contrasts with high expression in surrounding floral organs. (A) Structure of the male inflorescence of maize (image, J. Saunders; art, K. E. Koch). (B) Gene expression in floral organs and developing pollen. RNA was quantified by qRT-PCR (see Methods). Late-binucleate stage pollen was isolated from developmentally staged anthers as described by Wen and Chase (1999). The Wx1 starch synthase was measured as a positive control for pollen gene expression. Error bars are standard error of the mean, n = 3.
Mentions: To determine whether thiamin biosynthetic genes are expressed in developing pollen, we analyzed thiamin gene expression in pollen grains isolated during the starch-filling stage of pollen development. Figure 5 shows quantification of Thi1, Thi2 and THIC expression in the organs of the male inflorescence (Figure 5A); in binucleate-stage developing pollen; and in pre-anthesis stage anthers. The qRT-PCR results confirmed that expression of thiazole and pyrimidine biosynthetic genes is very low in both anthers and developing pollen in contrast to the high expression observed in rachis (stem of the male inflorescence) and rachilla and glume organs of the male flower. As a positive control, we assayed expression of Wx1, which is known to function in developing pollen (Nelson, 1962). As expected, developing anthers and pollen exhibited high relative expression of Wx1 supporting our conjecture that the starch biosynthetic pathway is down-regulated during pollen maturation most likely immediately prior to anthesis. By contrast, the de novo thiamin biosynthetic pathway is inactive in starch-filling pollen as well as mature pollen.

Bottom Line: By contrast, divergent patterns of THIC and THI4 expression occur in the shoot apical meristem, embyro sac, embryo, endosperm, and root-tips suggesting that these sink organs acquire significant amounts of thiamin via salvage pathways.Finally, stable isotope labeling experiments set an upper limit on the rate of de novo thiamin biosynthesis in maize leaf explants.Overall, the observed patterns of thiamin biosynthetic gene expression mirror the strategies for thiamin acquisition that have evolved in bacteria.

View Article: PubMed Central - PubMed

Affiliation: Genetics Institute and Horticultural Sciences Department, Institute of Food and Agricultural Sciences, University of Florida Gainesville, FL, USA.

ABSTRACT
The B vitamin thiamin is essential for central metabolism in all cellular organisms including plants. While plants synthesize thiamin de novo, organs vary widely in their capacities for thiamin synthesis. We use a transcriptomics approach to appraise the distribution of de novo synthesis and thiamin salvage pathways among organs of maize. We identify at least six developmental contexts in which metabolically active, non-photosynthetic organs exhibit low expression of one or both branches of the de novo thiamin biosynthetic pathway indicating a dependence on inter-cellular transport of thiamin and/or thiamin precursors. Neither the thiazole (THI4) nor pyrimidine (THIC) branches of the pathway are expressed in developing pollen implying a dependence on import of thiamin from surrounding floral and inflorescence organs. Consistent with that hypothesis, organs of the male inflorescence and flowers are shown to have high relative expression of the thiamin biosynthetic pathway and comparatively high thiamin contents. By contrast, divergent patterns of THIC and THI4 expression occur in the shoot apical meristem, embyro sac, embryo, endosperm, and root-tips suggesting that these sink organs acquire significant amounts of thiamin via salvage pathways. In the root and shoot meristems, expression of THIC in the absence of THI4 indicates a capacity for thiamin synthesis via salvage of thiazole, whereas the opposite pattern obtains in embryo and endosperm implying that seed storage organs are poised for pyrimidine salvage. Finally, stable isotope labeling experiments set an upper limit on the rate of de novo thiamin biosynthesis in maize leaf explants. Overall, the observed patterns of thiamin biosynthetic gene expression mirror the strategies for thiamin acquisition that have evolved in bacteria.

No MeSH data available.


Related in: MedlinePlus