Low iron ameliorates the salinity-induced growth cessation of seminal roots in wheat seedlings.

Wheat plants are ubiquitously simultaneously exposed to salinity and limited iron availability caused by soil saline-alkalisation. Through this study, we found that both low Fe and NaCl severely inhibited the growth of seminal roots in wheat seedlings; however, sufficient Fe caused greater growth cessation of seminal roots than low Fe under salt stress. Low Fe improved the root meristematic division activity, not altering the mature cell sizes compared with sufficient Fe under salt stress. Foliar Fe spray and split-root experiments showed that low Fe-alleviating the salinity-induced growth cessation of seminal roots was dependent on local low Fe signals in the roots. Ionomics combined with TEM/X-ray few differences in the root Na+ uptake and vacuolar Na+ sequestration between two Fe levels under salt stress. Phytohormone profiling and metabolomics revealed salinity-induced overaccumulation of ACC/ethylene and tryptophan/auxin in the roots under sufficient Fe than under low Fe. Differential gene expression, pharmacological inhibitor addition and the root growth performance of transgenic wheat plants revealed that the rootward auxin efflux and was responsible for the low Fe-mediated amelioration of the salinity-induced growth cessation of seminal roots. Our findings will provide novel insights into the modulation of crop root growth under salt stress.

Genome-Scale Investigation of GARP Family Genes Reveals Their Pivotal Roles in Nutrient Stress Resistance in Allotetraploid Rapeseed.

The GARP genes are plant-specific transcription factors (TFs) and play key roles in regulating plant development and abiotic stress resistance. However, few systematic analyses of GARPs have been reported in allotetraploid rapeseed (Brassica napus L.) yet. In the present study, a total of 146 BnaGARP members were identified from the rapeseed genome based on the sequence signature. The BnaGARP TFs were divided into five subfamilies: ARR, GLK, NIGT1/HRS1/HHO, KAN, and PHL subfamilies, and the members within the same subfamilies shared similar exon-intron structures and conserved motif configuration. Analyses of the Ka/Ks ratios indicated that the GARP family principally underwent purifying selection. Several cis-acting regulatory elements, essential for plant growth and diverse biotic and abiotic stresses, were identified in the promoter regions of BnaGARPs. Further, 29 putative miRNAs were identified to be targeting BnaGARPs. Differential expression of BnaGARPs under low nitrate, ammonium toxicity, limited phosphate, deficient boron, salt stress, and cadmium toxicity conditions indicated their potential involvement in diverse nutrient stress responses. Notably, BnaA9.HHO1 and BnaA1.HHO5 were simultaneously transcriptionally responsive to these nutrient stresses in both hoots and roots, which indicated that BnaA9.HHO1 and BnaA1.HHO5 might play a core role in regulating rapeseed resistance to nutrient stresses. Therefore, this study would enrich our understanding of molecular characteristics of the rapeseed GARPs and will provide valuable candidate genes for further in-depth study of the GARP-mediated nutrient stress resistance in rapeseed.

Morpho-physiological, Genomic, and Transcriptional Diversities in Response to Potassium Deficiency in Rapeseed (Brassica napus L.) Genotypes.

Variations in the resistance to potassium (K) deficiency among rapeseed genotypes emphasize complicated regulatory mechanisms. In this study, a low-K-sensitivity accession (L49) responded to K deficiency with smaller biomasses, severe leaf chlorosis, weaker photosynthesis ability, and deformed stomata morphology compared to a low-K resistant accession (H280). H280 accumulated more K+ than L49 under low K. Whole-genome resequencing (WGS) revealed a total of 5,538,622 single nucleotide polymorphisms (SNPs) and 859,184 insertions/deletions (InDels) between H280 and L49. RNA-seq identified more differentially expressed K+ transporter genes with higher expression in H280 than in L49 under K deficiency. Based on the K+ profiles, differential expression profiling, weighted gene coexpression network analysis, and WGS data between H280 and L49, BnaC4.AKT1 was proposed to be mainly responsible for root K absorption-mediated low K resistance. BnaC4.AKT1 was expressed preferentially in the roots and localized on the plasma membrane. An SNP and an InDel found in the promoter region of BnaC4.AKT1 were proposed to be responsible for its differential expression between rapeseed genotypes. This study identified a gene resource for improving low-K resistance. It also facilitates an integrated knowledge of the differential physiological and transcriptional responses to K deficiency in rapeseed genotypes.

Differential Morpho-Physiological, Ionomic, and Phytohormone Profiles, and Genome-Wide Expression Profiling Involving the Tolerance of Allohexaploid Wheat (Triticum aestivum L.) to Nitrogen Limitation.

Common wheat (Triticum aestivum L.) is a global staple food, while nitrogen (N) limitation severely hinders plant growth, seed yield, and grain quality of wheat. Genetic variations in the responses to low N stresses among allohexaploid wheat (AABBDD, 2n = 6x = 42) genotypes emphasize the complicated regulatory mechanisms underlying low N tolerance and N use efficiency (NUE). In this study, hydroponic culture, inductively coupled plasma mass spectrometry, noninvasive microtest, high-performance liquid chromatography, RNA-seq, and bioinformatics were used to determine the differential growth performance, ionome and phytohormone profiles, and genome-wide expression profiling of wheat plants grown under high N and low N conditions. Transcriptional profiling of NPFs, NRT2s, CLCs, SLACs/SLAHs, AAPs, UPSs, NIAs, and GSs characterized the core members, such as TaNPF6.3-6D, TaNRT2.3-3D, TaNIA1-6B, TaGLN1;2-4B, TaAAP14-5A/5D, and TaUPS2-5A, involved in the efficient transport and assimilation of nitrate and organic N nutrients. The low-N-sensitivity wheat cultivar XM26 showed obvious leaf chlorosis and accumulated higher levels of ABA, JA, and SA than the low-N-tolerant ZM578 under N limitation. The TaMYB59-3D-TaNPF7.3/NRT1.5-6D module-mediated shoot-to-root translocation and leaf remobilization of nitrate was proposed as an important pathway regulating the differential responses between ZM578 and XM26 to low N. This study provides some elite candidate genes for the selection and breeding of wheat germplasms with low N tolerance and high NUE.