The legwd mutant uncovers the role of starch phosphorylation in pollen development and germination in tomato

Starches extracted from most plant species are phosphorylated. α-Glucan water dikinase (GWD) is a key enzyme that controls the phosphate content of starch. In the absence of its activity starch degradation is impaired, leading to a starch excess phenotype in Arabidopsis and in potato leaves, and to reduced cold sweetening in potato tubers. Here, we characterized a transposon insertion ( legwd::Ds ) in the tomato GWD ( LeGWD ) gene that caused male gametophytic lethality. The mutant pollen had a starch excess phenotype that was associated with a reduction in pollen germination. SEM and TEM analyses indicated mild shrinking of the pollen grains and the accumulation of large starch granules inside the plastids. The level of soluble sugars was reduced by 1.8-fold in mutant pollen grains. Overall, the transmission of the mutant allele was only 0.4% in the male, whereas it was normal in the female. Additional mutant alleles, obtained through transposon excision, showed the same phenotypes as legwd::Ds . Moreover, pollen germination could be restored, and the starch excess phenotype could be abolished in lines expressing the potato GWD homolog ( StGWD ) under a pollen-specific promoter. In these lines, where fertility was restored, homozygous plants for legwd::Ds were isolated, and showed the starch excess phenotype in the leaves. Overall, our results demonstrate the importance of starch phosphorylation and breakdown for pollen germination, and open up the prospect for analyzing the role of starch metabolism in leaves and fruits.     

Sivb 2003 Congress Symposium Proceeding: Mutation- and Transposon-Based Approaches for the Identification of Genes for Pre-Harvest Sprouting in Wheat

Summary This article reviews techniques for gene identification and cloning in allohexaploid bread wheat (Triticum aestivum L.). Gene identification and cloning in wheat are complicated by the large size and high redundancy of the genome. Both classical mutagenesis and transposon tagging are important tools for the study of grain dormancy and plant hormone signaling in wheat. While classical mutagenesis can be used to identify wheat mutants with altered hormone sensitivity, it can be difficult to clone the corresponding genes. We review the techniques available for gene identification in wheat, and propose that transposon-based activation tagging will be an important tool for wheat genetics.