Considerable genetic variation in agronomic nitrogen (N) use efficiency (NUE) has been reported among genotypes of Brassica napus. However, the physiological and molecular mechanisms underpinning these differences remain poorly understood. In this study, physiological and genetic factors impacting NUE were identified in field trials and hydroponic experiments using two B. napus genotypes with contrasting NUE. The results showed that the N‐efficient genotype (D4‐15) had greater N uptake and utilization efficiencies, more root tips, larger root surface and root volume, and higher N assimilation and photosynthesis capacity than the N‐inefficient genotype (D2‐1). Genomic analysis revealed that D4‐15 had a greater genome diversity related to NUE than D2‐1. By combining genomic and transcriptomic analysis, genes involved in photosynthesis and C/N metabolism were implicated in conferring NUE. Co‐expression network analysis of genes that differed between the two genotypes suggested gene clusters impacting NUE. A nitrate transporter gene BnaA06g04560D (NRT2.1) and two vacuole nitrate transporter CLC genes (BnaA02g11800D and BnaA02g28670D) were up‐regulated by N starvation in D4‐15 but not in D2‐1. The study revealed that high N uptake and utilization efficiencies, maintained photosynthesis and coordinated C/N metabolism confer high NUE in B. napus, and identified candidate genes that could facilitate breeding for enhanced NUE in B. napus.
Summary
Brassinosteroids (BRs) are pivotal phytohormones involved in the control of root development. Boron (B) is an essential micronutrient for plants, and root growth is rapidly inhibited under B deficiency conditions. However, the mechanisms underlying this inhibition are still unclear. Here, we identified BR‐related processes underlying B deficiency at the physiological, genetic, molecular/cell biological and transcriptomic levels and found strong evidence that B deficiency can affect BR biosynthesis and signalling, thereby altering root growth. RNA sequencing analysis revealed strong co‐regulation between BR‐regulated genes and B deficiency‐responsive genes. We found that the BR receptor mutants bri1‐119 and bri1‐301 were more insensitive to decreased B supply, and the gain‐of‐function mutants bes1‐D and pBZR1‐bzr1‐D exhibited insensitivity to low‐B stress. Under B deficiency conditions, exogenous 24‐epibrassinolide rescued the inhibition of root growth, and application of the BR biosynthesis inhibitor brassinazole exacerbated this inhibitory effect. The nuclear‐localised signal of BES1 was reduced under low‐B conditions compared with B sufficiency conditions. We further found that B deficiency hindered the accumulation of brassinolide to downregulate BR signalling and modulate root elongation, which may occur through a reduction in BR6ox1 and BR6ox2 mRNA levels. Taken together, our results reveal a role of BR signalling in root elongation under B deficiency.
Brassinosteroid (BR) is a pivotal phytohormone involved in regulating root development. Boron (B) is an essential micronutrient for plant growth and development, and root growth of plants is rapidly inhibited under B deficiency condition, but the mechanisms are still elusive. Here, we demonstrate that BR plays crucial roles in these processes. We identify BR-related processes underlying B deficiency at the physiological, genetic, molecular/cell biological and transcriptome levels, and provide strong evidences that B deficiency can affect BR signalling, thereby altering root growth. RNA-sequencing analysis reveals a high co-regulation between BR-regulated genes and B deficiency-responsive genes. We found that low B negatively regulates BR signalling to control BR signalling-dependent root elongation, bes1-D exhibits insensitivity to low B stress, and bri1-301 mutants fails to respond to B depletion. Exogenous eBL application can rescue the inhibition of root growth under B deficiency condition, and application of BR biosynthesis inhibitor BRZ aggravates root growth inhibition of wild-type under B deficiency condition. B deficiency reduces the nuclear signal of BES1. We further found that B deficiency reduces the accumulation of brassinolide (BL) by reducing BR6ox1 and BR6ox2 mRNA level to down-regulate BR signalling and modulate root elongation. Altogether, our results uncover a role of BR signalling in root elongation under B deficiency.One-sentence summaryB deficiency reduces the accumulation of brassinolide by reducing BR6ox1 and BR6ox2 mRNA level to down-regulate BR signalling and modulate root elongation.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.