Molecular and physiological mechanisms of tea (Camellia sinensis (L.) O. Kuntze) leaf and root in response to nitrogen deficiency.

Background: As an economically important crop, tea is strongly nitrogen (N)-dependent. However, the physiological and molecular mechanisms underlying the response of N deficiency in tea are not fully understood. Tea cultivar "Chunlv2" [Camellia sinensis (L.) O. Kuntze] were cultured with a nutrient solution with 0 mM [N-deficiency] or 3 mM (Control) NHNO in 6 L pottery pots containing clean river sands.

Results: N deficiency significantly decreased N content, dry weight, chlorophyll (Chl) content, L-theanine and the activities of N metabolism-related enzymes, but increased the content of total flavonoids and polyphenols in tea leaves. N deficiency delayed the sprouting time of tea buds. By using the RNA-seq technique and subsequent bioinformatics analysis, 3050 up-regulated and 2688 down-regulated differentially expressed genes (DEGs) were isolated in tea leaves in response to N deficiency. However, only 1025 genes were up-regulated and 744 down-regulated in roots. Gene ontology (GO) term enrichment analysis showed that 205 DEGs in tea leaves were enriched in seven GO terms and 152 DEGs in tea roots were enriched in 11 GO items based on P < 0.05. In tea leaves, most GO-enriched DEGs were involved in chlorophyll a/b binding activities, photosynthetic performance, and transport activities. But most of the DEGs in tea roots were involved in the metabolism of carbohydrates and plant hormones with regard to the GO terms of biological processes. N deficiency significantly increased the expression level of phosphate transporter genes, which indicated that N deficiency might impair phosphorus metabolism in tea leaves. Furthermore, some DEGs, such as probable anion transporter 3 and high-affinity nitrate transporter 2.7, might be of great potential in improving the tolerance of N deficiency in tea plants and further study could work on this area in the future.

Conclusions: Our results indicated N deficiency inhibited the growth of tea plant, which might be due to altered N metabolism and expression levels of DEGs involved in the photosynthetic performance, transport activity and oxidation-reduction processes.