A Chromosome-level Genome Assembly Provides Insights into the Local Adaptation of Tamarix austromongolica in the Yellow River Basin, China.

Tamarix austromongolica is endemic to the Yellow River Basin and has adapted to diverse ecological settings in the region, including the arid areas of northwestern China and the saline soil regions of the Yellow River Delta. However, the genetic basis of its local adaptation remains unclear. We report a chromosome-level assembly of the T. austromongolica genome based on PacBio high-fidelity sequencing and Hi-C technology. The 12 pseudochromosomes cover 98.44% of the 1.32 Gb assembly, with a contig N50 of 52.57 Mb and a BUSCO score of 98.2%. The genome comprises 913.6 Mb (68.83%) of repetitive sequences and 22,374 protein-coding genes. Genome evolution analyses suggest that genes under positive selection and significantly expanded gene families have facilitated T. austromongolica's adaptability to diverse environmental factors and high resistance to diseases. Using genotyping-by-sequencing, we conducted population structure and selection analyses of 114 samples from 15 sites. Two genetic groups were identified, and 114 and 289 candidate genes were assigned to the populations of the northwestern and eastern parts of the Yellow River, respectively. Furthermore, we discovered numerous candidate genes associated with high-altitude adaptability and salt tolerance. This research provides valuable genomic resources for the evolutionary study and genetic breeding of tamarisk.

Phenylalanine as a nitrogen source induces root growth and nitrogen-use efficiency in Populus × canescens.

To investigate the physiological responses of poplars to amino acids as sole nitrogen (N) sources, Populus × canescens (Ait.) Smith plants were supplied with one of three nitrogen fertilizers (NH4NO3, phenylalanine (Phe) or the mixture of NH4NO3 and Phe) in sand culture. A larger root system, and decreased leaf size and CO2 assimilation rate was observed in Phe- versus NH4NO3-treated poplars. Consistently, a greater root biomass and a decreased shoot growth were detected in Phe-supplied poplars. Decreased enzymatic activities of nitrate reductase (NR), glutamate synthase (GOGAT) and glutamate dehydrogenase (GDH) and elevated activities of nitrite reductase (NiR), phenylalanine ammonia lyase (PAL), glutamine synthetase (GS) and asparagine synthase (AS) were found in Phe-treated roots. Accordingly, reduced concentrations of NH4+, NO3- and total N, and enhanced N-use efficiencies (NUEs) were detected in Phe-supplied poplars. Moreover, the transcript levels of putative Phe transporters ANT1 and ANT3 were upregulated, and the mRNA levels of NR, glutamine synthetase 2 (GS2), NADH-dependent glutamate synthase (NADH-GOGAT), GDH and asparagine synthetase 2 (ASN2) were downexpressed in Phe-treated roots and/or leaves. The 15N-labeled Phe was mainly allocated in the roots and only a small amount of 15N-Phe was translocated to poplar aerial parts. These results indicate that poplar roots can acquire Phe as an N source to support plant growth and that Phe-induced NUEs in the poplars are probably associated with NH4+ re-utilization after Phe deamination and the carbon bonus simultaneously obtained during Phe uptake.

Phosphorus and nitrogen physiology of two contrasting poplar genotypes when exposed to phosphorus and/or nitrogen starvation.

Phosphorus (P) and nitrogen (N) are the two essential macronutrients for tree growth and development. To elucidate the P and N physiology of woody plants during acclimation to P and/or N starvation, we exposed saplings of the slow-growing Populus simonii Carr (Ps) and the fast-growing Populus × euramericana Dode (Pe) to complete nutrients or starvation of P, N or both elements (NP). P. × euramericana had lower P and N concentrations and greater P and N amounts due to higher biomass production, thereby resulting in greater phosphorus use efficiency/N use efficiency (PUE/NUE) compared with Ps. Compared with the roots of Ps, the roots of Pe exhibited higher enzymatic activities in terms of acid phosphatases (APs) and malate dehydrogenase (MDH), which are involved in P mobilization, and nitrate reductase (NR), glutamate synthase (GOGAT) and glutamate dehydrogenase (GDH), which participate in N assimilation. The responsiveness of the transcriptional regulation of key genes encoding transporters for phosphate, ammonium and nitrate was stronger in Pe than in Ps. These results suggest that Pe possesses a higher capacity for P/N uptake and assimilation, which promote faster growth compared with Ps. In both poplars, P or NP starvation caused significant decreases in the P concentrations and increases in PUE. Phosphorus deprivation induced the activity levels of APs, phosphoenolpyruvate carboxylase and MDH in both genotypes. Nitrogen or NP deficiency resulted in lower N concentrations, amino acid levels, NR and GOGAT activities, and higher NUE in both poplars. Thus, in Ps and Pe, the mRNA levels of PHT1;5, PHT1;9, PHT2;1, AMT2;1 and NR increased in the roots, while PHT1;9, PHO1;H1, PHO2, AMT1;1 and NRT2;1 increased in the leaves during acclimation to P, N or NP deprivation. These results suggest that both poplars suppress P/N uptake, mobilization and assimilation during acclimation to P, N or NP starvation.