Transcriptome profiling of Puccinellia tenuiflora during seed germination under a long-term saline-alkali stress

Abstract

Puccinellia tenuiflora is the most saline-alkali tolerant plant in the Songnen Plain, one of the three largest soda saline-alkali lands worldwide. Here, we investigated the physicochemical properties of saline-alkali soils from the Songnen Plain and sequenced the transcriptomes of germinated P. tenuiflora seedlings under long-term treatment (from seed soaking) with saline-alkali soil extracts. We found that the soils from Songnen Plain were reasonably rich in salts and alkali; moreover, the soils were severely deficient in nitrogen [N], phosphorus [P], potassium [K] and several other mineral elements. This finding demonstrated that P. tenuiflora can survive from not only high saline-alkali stress but also a lack of essential mineral elements. To explore the saline-alkali tolerance mechanism, transcriptional analyses of P. tenuiflora plants treated with water extracts from the saline-alkali soils was performed. Interestingly, unigenes involved in the uptake of N, P, K and the micronutrients were found to be significantly upregulated, which indicated the existence of an efficient nutrition-uptake system in P. tenuiflora . Compared with P. tenuiflora , the rice Oryza sativa was hypersensitive to saline-alkali stress. The results obtained using a noninvasive microtest techniques confirmed that the uptake of NO 3 - and NH 4 + and the regulatory flux of Na + and H + were significantly higher in the roots of P. tenuiflora than in those of O. sativa . In the corresponding physiological experiments, the application of additional nutrition elements significantly eliminated the sensitive symptoms of rice to saline-alkali soil extracts. Our results imply that the survival of P. tenuiflora in saline-alkali soils is due to a combination of at least two regulatory mechanisms and the high nutrient uptake capacity of P. tenuiflora plays a pivotal role in its adaptation to those stress. Taken together, our results highlight the role of nutrition uptake in saline-alkali stress tolerance in plants.