Cytokinins as boron deficiency signals to sustain shoot development in boron-efficient oilseed rape

Transcriptome and phytohormone profiling of stamen and pistil in Brassica napus under boron deficiency

Plant reproduction is a fundamental requirement for plants to sustain genetic inheritance. In the perspective of plant nutrition, such process is strongly influenced by boron deficiency (-B) and as documented about a century ago. To date, little is known about the mechanism of boron deficiency-induced fertility reduction. In this study, we successfully established a cultivation system for Brassica napus to precisely manipulate boron supply when the generative stage initiates. We dissected the stamen and pistil of early-developing Brassica napus flower buds for transcriptome and phytohormone analysis, and demonstrated pistil and stamen showed distinct responding processes to -B. In addition, we revealed that auxin (IAA)-related compounds and several IAA-biosynthesis genes may play important roles in reproductive organ responding to -B, suggesting the IAA metabolism pathway seems to play a crucial role in -B induced reproductive organ abortion process. Taken together, we created a reliable system to study boron deficiency induced fertility reduction, by which generated the first transcriptome result for dissected stamen and pistil under different boron regimes, and suggested IAA metabolism pathway deserves as important target for further study in such regimes.

Association of the benzoxazinoid pathway with boron homeostasis in maize

Both deficiency and toxicity of the micronutrient boron lead to severe reductions in crop yield. Despite this agricultural importance, the molecular basis underlying boron homeostasis in plants remains unclear. To identify molecular players involved in boron homeostasis in maize (Zea mays L.), we measured boron levels in the Goodman-Buckler association panel and performed genome-wide association studies. These analyses identified a benzoxazinless (bx) gene, bx3, involved in the biosynthesis of benzoxazinoids, such as 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA), which are major defense compounds in maize. Genes involved in DIMBOA biosynthesis are all located in close proximity in the genome, and benzoxazinoid biosynthesis mutants, including bx3, are all DIMBOA deficient. We determined that leaves of the bx3 mutant have a greater boron concentration than those of B73 control plants, which corresponded with enhanced leaf tip necrosis, a phenotype associated with boron toxicity. By contrast, other DIMBOA-deficient maize mutants did not show altered boron levels or the leaf tip necrosis phenotype, suggesting that boron is not associated with DIMBOA. Instead, our analyses suggest that the accumulation of boron is linked to the benzoxazinoid intermediates indolin-2-one (ION) and 3-hydroxy-ION. Therefore, our results connect boron homeostasis to the benzoxazinoid plant defense pathway through bx3 and specific intermediates, rendering the benzoxazinoid biosynthesis pathway a potential target for crop improvement under inadequate boron conditions.

Elucidating the callus-to-shoot-forming mechanism in Capsicum annuum 'Dempsey' through comparative transcriptome analyses

BACKGROUND

The formation of shoots plays a pivotal role in plant organogenesis and productivity. Despite its significance, the underlying molecular mechanism of de novo regeneration has not been extensively elucidated in Capsicum annuum 'Dempsey', a bell pepper cultivar. To address this, we performed a comparative transcriptome analysis focusing on the differential expression in C. annuum 'Dempsey' shoot, callus, and leaf tissue. We further investigated phytohormone-related biological processes and their interacting genes in the C. annuum 'Dempsey' transcriptome based on comparative transcriptomic analysis across five species.

RESULTS

We provided a comprehensive view of the gene networks regulating shoot formation on the callus, revealing a strong involvement of hypoxia responses and oxidative stress. Our comparative transcriptome analysis revealed a significant conservation in the increase of gene expression patterns related to auxin and defense mechanisms in both callus and shoot tissues. Consequently, hypoxia response and defense mechanism emerged as critical regulators in callus and shoot formation in C. annuum 'Dempsey'. Current transcriptome data also indicated a substantial decline in gene expression linked to photosynthesis within regenerative tissues, implying a deactivation of the regulatory system governing photosynthesis in C. annuum 'Dempsey'.

CONCLUSION

Coupled with defense mechanisms, we thus considered spatial redistribution of auxin to play a critical role in the shoot morphogenesis via primordia outgrowth. Our findings shed light on shoot formation mechanisms in C. annuum 'Dempsey' explants, important information for regeneration programs, and have broader implications for precise molecular breeding in recalcitrant crops.

Linking the key physiological functions of essential micronutrients to their deficiency symptoms in plants

In this review, we untangle the physiological key functions of the essential micronutrients and link them to the deficiency responses in plants. Knowledge of these responses at the mechanistic level, and the resulting deficiency symptoms, have improved over the last decade and it appears timely to review recent insights for each of them. A proper understanding of the links between function and symptom is indispensable for an accurate and timely identification of nutritional disorders, thereby informing the design and development of sustainable fertilization strategies. Similarly, improved knowledge of the molecular and physiological functions of micronutrients will be important for breeding programmes aiming to develop new crop genotypes with improved nutrient-use efficiency and resilience in the face of changing soil and climate conditions.

What Can Boron Deficiency Symptoms Tell Us about Its Function and Regulation?

On the eve of the 100th anniversary of Dr. Warington's discovery of boron (B) as a nutrient essential for higher plants, "boronists" have struggled to demonstrate a role beyond its structural function in cell walls dimerizing pectin molecules of rhamnogalacturonan II (RGII). In this regard, B deficiency has been associated with a plethora of symptoms in plants that include macroscopic symptoms like growth arrest and cell death and biochemical or molecular symptoms that include changes in cell wall pore size, apoplast acidification, or a steep ROS production that leads to an oxidative burst. Aiming to shed light on B functions in plant biology, we proposed here a unifying model integrating the current knowledge about B function(s) in plants to explain why B deficiency can cause such remarkable effects on plant growth and development, impacting crop productivity. In addition, based on recent experimental evidence that suggests the existence of different B ligands other than RGII in plant cells, namely glycolipids, and glycoproteins, we proposed an experimental pipeline to identify putative missing ligands and to determine how they would integrate into the above-mentioned model.