Molecular analyses of internode elongation and cold stress tolerance in maize
Modulation of internode elongation can impact maize (Zea mays L.) yield. In maize, plant height is often positively correlated with grain and biomass yields. Conversely, semi dwarf varieties have been used to achieve higher grain yields in wheat and sorghum by preventing lodging and by allocating more resources to grain filling instead of vegetative tissues. Tolerance to suboptimal temperatures is also a sought after trait in maize, as it would make possible to expand the cultivated areas to higher latitudes and allow for early planting, resulting in a longer growing season and higher yields. In this thesis I apply the tools and resources available since the publication of the first maize genome draft to investigate internode elongation and cold tolerance in maize. Using a forward genetics approach I identified GRMZM2G366698 (an inositol polyphosphate 5- phosphatase) as the gene affected by the mutation in brevis plant1 (bv1), a semi dwarf mutant of maize first reported in the 1930’s. Further characterization of bv1 and a study of the RNA transcript abundance differences between bv1 and wild type maize plants suggest that auxin mediated inositol polyphosphate and/or phosphoinositide signalling are implicated in maize stem elongation. I used RNA-Seq to investigate the transcriptional response of seedlings of cold tolerant CG60 and cold sensitive CG102 maize inbreds during cold stress and recovery after the cold stress. I found that the cold treatment caused changes in the expression of more than 40% of the genes expressed in leaves, with repression of genes involved in photosynthesis, and induction of genes involved in transcription regulation and protein phosphorylation. Transcript abundances observed 24 hours after returning to optimal growing temperature identified genes that could be involved in acclimation to cold or whose expression has been disrupted by the stress.