• Examining the physiological and genetic response of maize to low temperature conditions

      Di Fenza, Mauro; Teagasc Walsh Fellowship Programme (2013-01)
      Maize (Zea mays) is an emerging forage crop in Ireland, originating in warmer climates. Under Irish climate conditions establishment can be problematic due to low soil temperatures at early stages of establishment. Maize varieties with improved chilling tolerance have been developed and are on the market, but maize in Ireland is still established under plastic and further varietal improvements are required to make this crop more economically viable. To date, varieties are selected principally by phenotypic traits rather than genetic response. Investigation of the physiological and genetic response of maize towards cold/chilling stress at early developmental stage, in particular the response of developing maize roots to cold stress, can make a contribution towards the understanding of the molecular mechanisms conferring plant cold tolerance. The objectives of this study were aimed to create, at first, an experimental design to test the physiological response to low temperatures, under controlled environmental conditions, of various commercial maize cultivars adapted to grow in temperate climates. Responses to abiotic stresses such as cold involve changes in gene expression, therefore, once indentified the hybrids showing contrasting degrees of cold tolerance, these were profilied to examine gene expression and identify possible cold regulated genes. The physiological experiments on twelve maize varieties identified four genotypes with contrasting cold tolerance. Microarray analysis profiling these varieties was used to identify up and down regulated genes under cold/chilling conditions. The stress induced by the cold temperature in the genotypes Picker, PR39B29, Fergus and Codisco was reflected only on the expression profiles of the two varieties with superior cold tolerance, Picker and PR39B29. No significant changes in expression were observed in Fergus and Codisco in response to cold stress. The overall number of genes up and down regulated in the two cold tolerant varieties amounted to 69, which were, however, divided in a group of 39 genes in PR39B29 and 30 genes in Picker, as the two varieties exhibited two different trancriptomic patterns in which only four genes (RNA binding protein, pathogenesis-related protein 1 and two unknown proteins) were shared, although not all with the same degree of regulation. No cold regulated genes ware detected. The gene expression of the four-shared genes was further investigated with qRT-PCR in order to estimate the expression pattern over time. Five time points were used to analyse the expression trend of the genes. The gene expression was not maintained over the five time points, but it was subjected to fluctuation. However, with the exception of the RNA binding protein gene, the expression pattern was similar between the two varieties, indicating a common response to chilling stress.
    • Transcriptomic response of maize primary roots to low temperatures at seedling emergence

      Di Fenza, Mauro; Hogg, Bridget; Grant, Jim; Barth, Susanne; Department of Agriculture, Food and the Marine; RSF 07 501 (PeerJ, 2017-01-05)
      Background Maize (Zea mays) is a C4 tropical 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. Discussion 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.
    • Transcriptomic response of maize primary roots to low temperatures at seedling emergence

      Di Fenza, Mauro; Hogg, Bridget; Grant, Jim; Barth, Susanne; Irish Department of Agriculture, Food and the Marine; RSF 07 501 (PeerJ, 2017-01-05)
      Background. Maize (Zea mays) is a C4 tropical 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. Discussion. 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.