Transcriptomic response of maize primary roots to low temperatures at seedling emergence.
BACKGROUND
Maize (Zea mays) is a C4tropical cereal and its adaptation to temperate climates can be problematic due to low soil temperatures at early stages of establishment.


METHODS
In the current study we have firstly investigated the physiological response of twelve maize varieties, from a chilling condition adapted gene pool, to sub-optimal growth temperature during seedling emergence. To identify transcriptomic markers of cold tolerance in already adapted maize genotypes, temperature conditions were set below the optimal growth range in both control and low temperature groups. The conditions were as follows; control (18 °C for 16 h and 12 °C for 8 h) and low temperature (12 °C for 16 h and 6 °C for 8 h). Four genotypes were identified from the condition adapted gene pool with significant contrasting chilling tolerance.


RESULTS
Picker and PR39B29 were the more cold-tolerant lines and Fergus and Codisco were the less cold-tolerant lines. These four varieties were subjected to microarray analysis to identify differentially expressed genes under chilling conditions. Exposure to low temperature during establishment in the maize varieties Picker, PR39B29, Fergus and Codisco, was reflected at the transcriptomic level in the varieties Picker and PR39B29. No significant changes in expression were observed in Fergus and Codisco following chilling stress. A total number of 64 genes were differentially expressed in the two chilling tolerant varieties. These two varieties exhibited contrasting transcriptomic profiles, in which only four genes overlapped.


CONCLUSIONS
We observed that maize varieties possessing an enhanced root growth ratio under low temperature were more tolerant, which could be an early and inexpensive measure for germplasm screening under controlled conditions. We have identified novel cold inducible genes in an already adapted maize breeding gene pool. This illustrates that further varietal selection for enhanced chilling tolerance is possible in an already preselected gene pool.
College of Life Sciences, School of Biology and Environmental Sciences, University College Dublin, Dublin, Ireland; Crops, Environment & Land Use Programme, Crops Research Centre Oak Park, Teagasc, Carlow, Ireland.
Mauro
M
Di Fenza
College of Life Sciences, School of Biology and Environmental Sciences, University College Dublin , Dublin , Ireland.
Bridget
B
Hogg
Research Operations Group, Statistics and Applied Physics Department, Teagasc , Dublin , Ireland.
Jim
J
Grant
Crops, Environment & Land Use Programme, Crops Research Centre Oak Park, Teagasc , Carlow , Ireland.
Susanne
S
Barth
Chilling tolerance; Cold stress; Low temperature; Maize; Roots; Transcriptome