The NAM-B1 transcription factor and the control of grain composition in wheat

The NAM-B1 transcription factor increases grain protein content, alters grain micronutrient content and accelerates monocarpic senescence, often without imposing a yield penalty. The aim of this thesis was to understand the mechanisms by which NAM-B1 influences nutrient remobilisation and monocarpic senescence to cause these effects. To achieve this I have examined the expression patterns of NAM-B1 and its homologues during development. I have studied the effects of NAM-B1 on nutrient transport, photosynthetic capacity and grain filling using a range of molecular biology and physiological techniques. Finally to understand the network of genes which NAM-B1 regulates I have used chromatin-immunoprecipitation followed by next-generation sequencing (ChIP-seq) to identify downstream targets, and compared these to differentially expressed genes in plants with down-regulated expression of NAM-B1 homologues (NAM RNAi plants). I have found that NAM-B1 expression increases after anthesis in both vegetative and reproductive tissues, including the grain. In stem and leaf tissues I identified that NAM genes are highly expressed in the vascular bundles, which might be important for nutrient transport. However I did not find evidence for NAM genes altering xylem or phloem transport. I found that in NAM RNAi plants, grain development was decoupled from flag leaf senescence. In RNAi plants starch synthesis enzymes were less active during the middle of grain filling than in control plants, potentially resulting in the reallocation of photosynthate to the stems as water soluble carbohydrates. Many of the putative NAM-B1 target genes identified by ChIP-seq have functions related to photosynthesis and validation of these candidate genes is ongoing. In summary I have identified putative NAM-B1 target genes and found that NAM-B1 may act in a tissue specific manner to regulate monocarpic senescence and grain filling. Furthermore I have highlighted novel functions related to carbohydrate metabolism in stems and the grain.

Name dc:type.qualificationname

phd

Level dc:type.qualificationlevel

doctoral

Grantor dc:publisher.institution

University of East Anglia

Year dc:date.issued

2014

Author dc:creator

• Borrill, Philippa G.M.

Language dc:language

en