MADS-box (MADS) transcription factors (TFs) act as one of the largest TF families in plants. The members in this family play fundamental roles in almost every developmental process as well as involve plant responses to biotic and abiotic stresses. In this study, 54 of MADS genes in wheat, including 31 released publicly and 23 deposited as tentative consensus (TC) into GenBank database, were subjected to analyses of molecular characterization, expression pattern, and function under contrasting phosphate (Pi)-supply conditions. The 31 released MADS genes share cDNA full lengths of 683 to 1 297 bp, encoding amino acids of 170 to 274 aa that possess molecular weights of 19.21 to 31.33 kDa and isoelectric points of 5.74 to 9.63. Phylogenetic analysis categoried these wheat MADS genes into four subgroups containing 11, 5, 10, and 4 members, respectively. Under Pi sufficiency, the MADS genes showed drastically varied transcripts and they were categoried into expression groups of high, medium, low, and very low, respectively. Among them, several ones were differentially expressed under Pi deprivation, including that five were upregulated (TaMADS51, TaMADS4, TaMADS5, TaMADS6, and TaMADS18) and four were downregulated (TaMADAGL17, TaMADAGL2, TaMADWM31C, and TaMADS;14). qPCR analyses confirmed their expression patterns in responding to the Pi-starvation stress. TaMADS51, one of the upregulated genes by Pi deprivation, was subjected to the functional analysis in mediating plant tolerance to the Pi-starvation stress. The transgenic tobocco plants overexpressing TaMADS51 exhibited much more improved growth features, drymass, Pi acquisition, and photosynthetic parameters as well as antioxidant enzymatic activities under Pi deprivation than wild type. These results indicate that distinct MADS genes are transcriptional response to Pi deprivation and play critical roles in mediating plant tolerance to this stressor through regulating downstream Pi-responsive genes.

In this study, 14 wheat cultivars with contrasting yield and N use efficiency (NUE) were used to investigate the agronomic and NUE-related traits, and the N assimilation-associated enzyme activities under low and high N conditions. Under deficient-N, the cultivars with high N uptake efficiency (UpE) and high N utilization efficiency (UtE) exhibited higher plant biomass, yields, and N contents than those with medium and low NUEs. The high UpE cultivars accumulated more N than other NUE type cultivars. Under sufficient-N, the tested cultivars showed similar patterns in biomass, yield, and N content to those under deficient-N, but the varietal variations in above traits were smaller. In addition, the high UpE cultivars displayed much more of root biomass and larger of root length, surface area, and volume than other NUE type cultivars, indicating that the root morphological traits under N deprivation are closely associated with the plant biomass through its improvement of the N acquisition. The high UtE cultivars showed higher activities of nitrate reductase (NR), nitrite reductase (NIR), and glutamine synthetase (GS) at stages of seediling, heading and filling than other NUE type cultivars under both low and high N conditions. Moreover, the high UpE and UtE cultivars also displayed higher photosynthetic rate under deficient-N than the medium and low NUE cultivars. Together, our results indicated that the tested wheat cultivars possess dramatically genetic variations in biomass, yield, and NUE. The root morphological traits and the N assimilation enzymatic acitivities play critical roles in regulating N accumulation and internal N translocation under the N-starvation stress, respectively. They can be used as morphological and biochemical references for evaluation of UpE and UtE in wheat.