Final Activity Report Summary - CLAWS (Corn Leaf Acclimation to Water Stress: Towards uncovering the molecular network that controls cell division and expansion in the growth zone ...)
Drought limits crop growth potential in the field and causes considerable yield losses worldwide. Leaf growth and photosynthetic performance are particularly sensitive to low soil water availability. For these reasons, increased leaf tolerance to drought is a highly desirable trait for plant breeding programs.
Previous research revealed the importance of several physiological processes involved in growth responses to drought, including altered levels of specific phytohormones and the accumulation of specific metabolites protecting against dehydration. The genes involved in these responses are still poorly characterised, as well as the changes occurring in specific cell types.
This project was designed to improve our understanding of leaf responses to drought and discover new genes conferring tolerance to be used for production of future crop varieties. During my fellowship I combined the analysis of leaf growth dynamics at the organ and cellular level, i.e. cell proliferation and cell expansion, with extensive measurements of gene expression using maize leaves as a model system. Leaf growth resulted from the coordination of cell proliferation and cell expansion.
The project results showed that reduction of leaf growth during mild drought stress was due to both reduced number and activity of meristematic (stem) cells and due to impaired cell expansion. Because cell proliferation and cell expansion occurred in a linear gradient from the base to the tip of the leaf at distinct positions along the axis of a single maize leaf, I harvested samples at different positions from the leaf base. This simple idea resulted in enriched data with cells of different developmental age for the analysis of thousands of specific Ribonucleic acid (RNA) molecules by genome-wide profiling techniques such as complementary deoxyribonucleic acid amplified fragment length polymorphism (cDNA-AFLP) and microarray, or chip analysis.
In contrast with previous experiments that used the entire leaf for similar experiments, this approach revealed, for the first time to the best of my knowledge, distinct gene expression in proliferating and non-proliferating cells in maize leaves under both well-watered (control) and drought conditions. This was important because it allowed more precise identification of genes involved in the control of drought stress responses that would otherwise remain undetectable in whole leaf samples.
Using strict criteria for statistical significance, I identified a set of about 200 genes with increased or decreased expression at the RNA level as a consequence of drought in maize leaf proliferating cells. A similar number of genes were identified in expanding cells. These gene sets contained known components that controlled drought responses and, most importantly, novel ones which were not previously described, such as, for example, genes involved in protein biosynthesis and transcription factors. Key regulators of the leaf growth response to drought were included in the latter group of genes and were to be further analysed in greater detail in future work.
In summary, during this project I was successful in improving methodological aspects and contributing new knowledge to the field of leaf growth as a response to drought. Both these achievements would be useful in the future for basic and applied research aimed at enhancing yield stability of crops under unfavourable environmental conditions.
Previous research revealed the importance of several physiological processes involved in growth responses to drought, including altered levels of specific phytohormones and the accumulation of specific metabolites protecting against dehydration. The genes involved in these responses are still poorly characterised, as well as the changes occurring in specific cell types.
This project was designed to improve our understanding of leaf responses to drought and discover new genes conferring tolerance to be used for production of future crop varieties. During my fellowship I combined the analysis of leaf growth dynamics at the organ and cellular level, i.e. cell proliferation and cell expansion, with extensive measurements of gene expression using maize leaves as a model system. Leaf growth resulted from the coordination of cell proliferation and cell expansion.
The project results showed that reduction of leaf growth during mild drought stress was due to both reduced number and activity of meristematic (stem) cells and due to impaired cell expansion. Because cell proliferation and cell expansion occurred in a linear gradient from the base to the tip of the leaf at distinct positions along the axis of a single maize leaf, I harvested samples at different positions from the leaf base. This simple idea resulted in enriched data with cells of different developmental age for the analysis of thousands of specific Ribonucleic acid (RNA) molecules by genome-wide profiling techniques such as complementary deoxyribonucleic acid amplified fragment length polymorphism (cDNA-AFLP) and microarray, or chip analysis.
In contrast with previous experiments that used the entire leaf for similar experiments, this approach revealed, for the first time to the best of my knowledge, distinct gene expression in proliferating and non-proliferating cells in maize leaves under both well-watered (control) and drought conditions. This was important because it allowed more precise identification of genes involved in the control of drought stress responses that would otherwise remain undetectable in whole leaf samples.
Using strict criteria for statistical significance, I identified a set of about 200 genes with increased or decreased expression at the RNA level as a consequence of drought in maize leaf proliferating cells. A similar number of genes were identified in expanding cells. These gene sets contained known components that controlled drought responses and, most importantly, novel ones which were not previously described, such as, for example, genes involved in protein biosynthesis and transcription factors. Key regulators of the leaf growth response to drought were included in the latter group of genes and were to be further analysed in greater detail in future work.
In summary, during this project I was successful in improving methodological aspects and contributing new knowledge to the field of leaf growth as a response to drought. Both these achievements would be useful in the future for basic and applied research aimed at enhancing yield stability of crops under unfavourable environmental conditions.