Wheat grain development is characterized by remarkable trehalose 6-phosphate accumulation pregrain filling: tissue distribution and relationship to SNF1-related protein kinase1 activity - PubMed (original) (raw)

Eleazar Martínez-Barajas et al. Plant Physiol. 2011 May.

Abstract

Trehalose 6-phosphate (T6P) is a sugar signal that regulates metabolism, growth, and development and inhibits the central regulatory SNF1-related protein kinase1 (SnRK1; AKIN10/AKIN11). To better understand the mechanism in wheat (Triticum aestivum) grain, we analyze T6P content and SnRK1 activities. T6P levels changed 178-fold 1 to 45 d after anthesis (DAA), correlating with sucrose content. T6P ranged from 78 nmol g(-1) fresh weight (FW) pregrain filling, around 100-fold higher than previously reported in plants, to 0.4 nmol g(-1) FW during the desiccation stage. In contrast, maximum SnRK1 activity changed only 3-fold but was inhibited strongly by T6P in vitro. To assess SnRK1 activity in vivo, homologs of SnRK1 marker genes in the wheat transcriptome were identified using Wheat Estimated Transcript Server. SnRK1-induced and -repressed marker genes were expressed differently pregrain filling compared to grain filling consistent with changes in T6P. To investigate this further maternal and filial tissues were compared pre- (7 DAA) and during grain filling (17 DAA). Strikingly, in vitro SnRK1 activity was similar in all tissues in contrast to large changes in tissue distribution of T6P. At 7 DAA T6P was 49 to 119 nmol g(-1) FW in filial and maternal tissues sufficient to inhibit SnRK1; at 17 DAA T6P accumulation was almost exclusively endospermal (43 nmol g(-1) FW) with 0.6 to 0.8 nmol T6P g(-1) FW in embryo and pericarp. The data show a correlation between T6P and sucrose overall that belies a marked effect of tissue type and developmental stage on T6P content, consistent with tissue-specific regulation of SnRK1 by T6P in wheat grain.

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Figures

Figure 1.

Figure 1.

T6P and S6P contents in whole grains during wheat grain development 1 to 45 DAA. Means of four biological replicates with

se

of mean.

Figure 2.

Figure 2.

Amounts of sugars, sugar phosphates, and UDP-Glc in whole grains during wheat grain development 1 to 45 DAA. A, Glc, Fru, and Suc. B, Glc 6-P, Fru 6-P, Glc 1-P, and UDP-Glc. Means of four biological replicates with

se

of mean.

Figure 3.

Figure 3.

Correlation between T6P, sugars, and sugar phosphates and UDP-Glc. A, T6P and Suc. B, S6P and Suc. C, T6P and Glc and Fru. D, T6P and UDP-Glc.

Figure 4.

Figure 4.

SnRK1 activity in whole grains during wheat grain development. A, Between 1 and 45 DAA using AMARA and SPS peptide as substrate. B, Between 1 and 45 DAA using AMARA and SPS peptide as substrate in the presence of 1 m

m

T6P in the assay expressed as percent inhibition. C, At 5 DAA using AMARA and SPS peptide as substrate in the presence of between 5 μ

m

and 1 m

m

T6P. D, At 30 DAA using AMARA and SPS peptide as substrate in the presence of between 5 μ

m

and 1 m

m

T6P. Means of four biological replicates with

se

of mean.

Figure 5.

Figure 5.

SnRK1 target gene transcript abundance. Transcript abundance of wheat Affymetrix probesets corresponding to sets of 600 SnRK1-induced and 600 SnRK1-repressed Arabidopsis genes according to Baena-González et al. (2007) determined using WhETS tool (Mitchell et al., 2007). Log of normalized expression (i.e. divided by the median expression for that probeset) was averaged and

se

calculated. The resulting averages with

se

are displayed, back transformed to a linear scale. The 300 most abundantly expressed SnRK1-induced and 300 most abundantly SnRK1-repressed genes are presented.

Figure 6.

Figure 6.

Transcript abundance of trehalose pathway genes during grain development. A, Class I TPS, Bradi2g19640. B, Class II TPS, Bradi1g69420 (○) and Bradi4g29730 (•; TPS6), Bradi2g49870 (▾) and Bradi2g19710 (△; TPS7), and Bradi3g53790 (▪; TPS11). C, TPP genes most closely related to Arabidopsis TPPA, Bradi3g50810 (•), Bradi3g32970 (○). D, TPP from the distinct clade of TPP genes found in grasses, Bradi1g21420 (•), Bradi4g29030 (○).

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