Transcriptome and Metabolome Analyses Reveal Potential Salt Tolerance Mechanisms Contributing to Maintenance of Water Balance by the Halophytic Grass Puccinellia nuttalliana

Elevated soil salinity exacerbated by human activities and global climate change poses serious threats to plant survival. Although halophytes provide many important clues concerning salt tolerance in plants, some unanswered questions remain to be addressed, including the processes of water and solute transport regulation. We performed high-throughput RNA-sequencing in roots and metabolome characterizations in roots and leaves of Puccinellia nuttalliana halophytic grass subjected to 0 (control) and 150 mM NaCl. In RNAseq, a total of 31 Gb clean bases generated were de novo assembled into 941,894 transcripts. The PIP2;2 and HKT1;5 transcript levels increased in response to the NaCl treatment implying their roles in water and ion homeostasis. Several transcription factors, including WRKY39, DEK3, HY5, and ABF2, were also overexpressed in response to NaCl. The metabolomic analysis revealed that proline and dopamine significantly increased due to the upregulation of the pathway genes under salt stress, likely contributing to salt tolerance mechanisms. Several phosphatidylcholines significantly increased in roots suggesting that the alterations of membrane lipid composition may be an important strategy in P. nuttalliana for maintaining cellular homeostasis and membrane integrity under salt stress. In leaves, the TCA cycle was enriched suggesting enhanced energy metabolism to cope with salt stress. Other features contributing to the ability of P. nuttalliana to survive under high salinity conditions include salt secretion by the salt glands and enhanced cell wall lignification of the root cells. While most of the reported transcriptomic, metabolomics, and structural alterations may have consequences to water balance maintenance by plants under salinity stress, the key processes that need to be further addressed include the role of the changes in the aquaporin gene expression profiles in the earlier reported enhancement of the aquaporin-mediated root water transport.

Morphological and agronomic variation of Puccinellia nuttalliana populations from the Canadian Great Plains

Liu, Y. and Coulman, B. E. 2015. Morphological and agronomic variation of Puccinellia nuttalliana populations from the Canadian Great Plains. Can. J. Plant Sci. 95: 67–76. Native grass species are adapted to local environments and have the potential for development as forage or turf grass cultivars for semiarid environments. Nuttall's alkali grass [Puccinellia nuttalliana (Shultes) Hitchc.] is a salt-tolerant grass with potential for forage or turf use, and is widely distributed across western North America. Understanding the morphological and agronomic variability of this species is a prerequisite for developing populations suitable for dry and saline regions of western Canada. A collection of 24 Puccinellia nuttalliana populations from the provinces of Manitoba, Saskatchewan and Alberta were established in a field nursery in Saskatoon, Saskatchewan. Plant height, crown diameter, tiller number, seed yield, dry matter yield, leaf colour, leaf length, leaf width, spring growth and late summer regrowth of individual plants or plots were measured for each collection in 2011 and 2012. Significant variation was found among the 24 populations for all measured characters in both years. The populations Eston and Westbourne09 had taller plants with greater basal diameter, high tiller number, and high seed and dry matter yields, which suggest they may be useful for forage purposes. The population St. Denis had shorter plants with more tillers, greater basal diameter darker green leaf colour and high seed yields; thus, it may useful as a turfgrass. Within certain populations, individual genotypes were identified which would have potential for production of synthetic cultivars for forage or turf purposes. Cluster analysis was conducted using the unweighted pair group method with arithmetic mean (UPGMA) and principal coordinate analysis (PCoA). These analyses showed six distinct groups within the collected populations; however, there was no distinguishable pattern of clustering of populations by region.

Evaluating genetic variation and relationships among Puccinellia nuttalliana populations using amplified fragment length polymorphism markers

Liu, Y., Fu, Y.-B. and Coulman, B. E. 2013. Evaluating genetic variation and relationships among Puccinellia nuttalliana populations using amplified fragment length polymorphism markers. Can. J. Plant Sci. 93: 1097–1104. Nuttall's salt-meadow, or alkali grass [Puccinellia nuttalliana (Shultes) Hitchc.], is a native grass species in North America, well known for its salt tolerance. Little information is available about the genetic diversity of natural populations of this species. Amplified fragment length polymorphism (AFLP) markers were used to examine the inter-population relationships and to compare variances within and among 23 populations collected from the Canadian Great Plains. Five AFLP primer pairs were employed to screen 15 genotypes (five sets of three half-sib plants) from each population, and 185 polymorphic AFLP bands were scored for each sample. The frequencies of these scored bands ranged from 0.02 to 0.99 with a mean of 0.60. The analysis of molecular variance revealed more than 96% of the total AFLP variation resided within populations. Populations were not highly differentiated with only 4% of the total AFLP variation residing among populations. A Mantel test revealed a significant but low correlation between genetic and geographic distances (r=0.29, P=0.024). Implications for P. nuttalliana conservation, germplasm sampling, and cultivar development are discussed.