Combining single-cell RNA sequencing with spatial transcriptome analysis reveals dynamic molecular maps of cambium differentiation in the primary and secondary growth of trees

Primary and secondary growth of the tree stem are responsible for corresponding increases in trunk height and diameter.However,our molecular understanding of the biological processes that underlie these two types of growth is incomplete.In this study,we used single-cell RNA sequencing and spatial transcriptome sequencing to reveal the transcriptional landscapes of primary and secondary growth tissues in the Populus stem.Comparison between the cell atlas and differentiation trajectory of primary and secondary growth revealed different regulatory networks involved in cell differentiation from cambium to xylem precursors and phloem precursors.These regulatory networks may be controlled by auxin accumulation and distribution.Analysis of cell differentiation trajectories suggested that vessel and fiber development followed a sequential pattern of progressive transcriptional regulation.This research provides new insights into the processes of cell identity and differentiation that occur throughout primary and secondary growth of tree stems,increasing our understanding of the cellular differentiation dynamics that occur during stemgrowth in trees.

Transcriptional Regulation of Secondary Growth and Wood Formation

Secondary growth and wood formation are products of the vascular cambium, a lateral meristem. Although the mechanisms have only recently begun to be uncovered, transcriptional regulation appears increasingly central to the regulation of secondary growth. The importance of transcriptional regulation is illustrated by the correlation of expression of specific classes of genes with related biological processes occurring at specific stages of secondary growth, including cell division, cell expansion, and cell differentiation. At the same time, transcription factors have been characterized that affect specific aspects of secondary growth, including regulation of the cambium and differentiation of cambial daughter cells. In the present review, we summarize evidence pointing to transcription as a major mechanism for regulation of secondary growth, and outline future approaches for comprehensively describing transcriptional networks underlying secondary growth.

TwoMADS-boxgenes regulate vascularcambium activity and secondary growth by modulating auxin homeostasis in Populus

In trees,stem secondary growth depends on vascular cambium proliferation activity and subsequent cell differentiation,in which an auxin concentration gradient across the cambium area plays a crucial role in regulating the process.However,the underlying molecular mechanismfor the establishment of auxin concentration is not fully understood.In this study,we identified two function-unknown MADS-box genes,VCM1 and VCM2,which are expressed specifically in the vascular cambium and modulate the subcellular homeostasis of auxin.Simultaneous knockdown of both VCM1 and VCM2 enhanced vascular cambium proliferation activity and subsequent xylem differentiation.Overexpression of VCM1 suppressed vascular cambium activity and wood formation by regulating PIN5 expression,which tuned the soluble auxin concentration in the vascular cambium area.This study reveals the role of VCM1 and VCM2 in regulating the proliferation activity of the vascular cambium and secondary growth by modulating the subcellular auxin homeostasis in Populus.

Enhanced efficiency and stability in Sn-based perovskite solar cells with secondary crystallization growth

The conversion efficiencies reported for Tin(Sn)halide-based perovskite solar cells(PSCs)fall a large gap behind those of lead halide-based PSCs,mainly because of poor film quality of the former.Here we report an efficient strategy based on a simple secondary crystallization growth(SCG)technique to improve film quality for tin halide-based PSCs by applying a series of functional amine chlorides on the perovskite surface.They were discovered to enhance the film crystallinity and suppress the oxidation of Sn^(2+)remarkably,hence reduce trap state density and non-irradiative recombination in the absorber films.Furthermore,the SCG film holds the band levels matching better with carrier transport layers and herein favoring charge extraction at the device interfaces.Consequently,a champion device efficiency of 8.07% was achieved alo ng with significant enhancements in VOC and JSC,in contrast to 5.35% of the control device value.Moreover,the SCG film-based devices also exhibit superior stability comparing with the control one.This work explicitly paves a novel and general strategy for developing high performance lead-free PSCs.

Synthesis of an IMF zeolite membrane for the separation of xylene isomer

The synthesis of a continuous IMF zeolite membrane was fabricated on tubular substrates by seeded growth for the first time. The straight channels of IMF zeolite with diameters of 0.53–0.59 nm are distinguishable for p-xylene from o-xylene molecules. Pure IMF-phase high-silica IM-5 zeolite seeds with uniform and fine crystal size were fabricated by a new sonication-assisted aging process. The seeds were coated on the support by dipcoating and induced the formation of continuous membrane. Separation performance in p-/o-xylene mixture was investigated at various temperature and pressure. The typical IM-5zeolite membrane had p-/o-xylene separation factor of 3.7. Our results suggest that IM-5 zeolite is a potentially good membrane material for the separation of xylene mixtures.

Genome-wide Expression Profiling in Seedlings of the Arabidopsis Mutant uro that is Defective in the Secondary Cell Wall Formation

Plant secondary growth is of tremendous importance, not only for plant growth and development but also for economic usefulness. Secondary tissues such as xylem and phloem are the conducting tissues in plant vascular systems, essentially for water and nutrient transport, respectively. On the other hand, products of plant secondary growth are important raw materials and renewable sources of energy. Although advances have been recently made towards describing molecular mechanisms that regulate secondary growth, the genetic control for this process is not yet fully understood. Secondary cell wall formation in plants shares some common mechanisms with other plant secondary growth processes. Thus, studies on the secondary cell wall formation using Arabidopsis may help to understand the regulatory mechanisms for plant secondary growth. We previously reported phenotypic characterizations of an Arabidopsis semi-dominant mutant, upright rosette （uro）, which is defective in secondary cell wall growth and has an unusually soft stem. Here, we show that lignification in the secondary cell wall in uro is aberrant by analyzing hypocotyl and stem. We also show genome-wide expression profiles of uro seedlings, using the Affymetrix GeneChip that contains approximately 24 000 Arabidopsis genes. Genes identified with altered expression levels include those that function in plant hormone biosynthesis and signaling, cell division and plant secondary tissue growth. These results provide useful information for further characterizations of the regulatory network in plant secondary cell wall formation.

Microstructure and secondary phases in epitaxial LaBaCo_2O_(5.5 + δ) thin films

Aberration-corrected scanning transmission electron microscopy was employed to investigate the microstructures and secondary phases in LaBaCo2O5.5＋δ（LBCO） thin films grown on SrTiO3 （STO） substrates. The as-grown films showed an epitaxial growth on the substrates with atomically sharp interfaces and orientation relationships of [100]LBCO//[100]STO and （001）LBCO//（001）STO. Secondary phases were observed in the films, which strongly depended on the sample fabrication conditions. In the film prepared at a temperature of 900 ℃, nano-scale CoO pillars nucleated on the substrate, and grew along the [001] direction of the film. In the film grown at a temperature of 1000 ℃, isolated nano-scale C0304 particles appeared, which promoted the growth of {111 } twinning structures in the film. The orientation relationships and the interfaces between the secondary phases and the films were illustrated, and the growth mechanism of the film was discussed.

功能型有机阳离子诱导实现CsPbI_(3)全无机钙钛矿三维至零维晶相转化与表面重构

铅卤钙钛矿太阳能电池兼具高效率和低成本的突出优势,近年来研究进展迅速、应用前景广阔,对于进一步推进光伏产业发展、实现碳中和目标具有重要意义.相比于有机无机杂化钙钛矿,CsPbI_(3)全无机钙钛矿具有更高的化学稳定性,但同时也面临着缺陷密度较高的挑战,制约了该组分电池器件效率的进一步提升.钙钛矿表面重构是一种降低缺陷密度的有效方法,但受限于全无机结构中铅碘八面体与铯离子之间较强的离子键作用,诱发无机钙钛矿表面二次生长的困难远高于杂化钙钛矿体系.本文通过选取辛基十二烷基二甲基铵这一特殊的季铵阳离子,成功实现了CsPbI_(3)钙钛矿薄膜的表面重构与三维至零维的原位晶相转化.在这种功能型季铵溴盐的诱导作用下,零维Cs_(4)bI_(6)在CsPbI_(3)薄膜的表面晶界处原位生成,有效钝化了缺陷,提高了结构稳定性.基于表面重构与缺陷钝化的无机钙钛矿太阳能电池获得了20.63%的高光电转换效率,实现了长期的高效稳定运行.

Diverse Roles of Strigolactones in Plant Development

With the discovery of strigolactones as root exudate signals that trigger parasitic weed seed germination, and then as a branching inhibitor and plant hormone, the next phase of strigolactone research has quickly revealed this hormone class as a major player in optimizing plant growth and development. From the early stages of plant evolution, it seems that strigolactones were involved in enabling plants to modify growth in order to gain advantage in competi- tion with neighboring organisms for limited resources. For example, a moss plant can alter its growth in response to strigolactones emanating from a neighbor. Within a higher plant, strigolactones appear to be involved in controlling the balance of resource distribution via strategic modification of growth and development. Most notably, higher plants that encounter phosphate deficiency increase strigolactone production, which changes root growth and promotes fungal symbiosis to enhance phosphate intake. The shoot also changes by channeling resources away from unessential leaves and branches and into the main stem and root system. This hormonal response is a key adaption that radically alters whole-plant architecture in order to optimize growth and development under diverse environmental conditions.

PtrHB7, a class III HD-Zip Gene, Plays a Critical Role in Regulation of Vascular Cambium Differentiation in Populus

A key question in the secondary growth of trees is how differentiation of the vascular cambium cells is directed to concurrently form two different tissues： xylem or phloem, class III homeodomain-leucine zipper （HD-Zip III） genes are known to play critical roles in the initiation, patterning, and differentiation of the vascular system in the process of primary and secondary growth. However, the mechanism of how these genes control secondary vascular dif- ferentiation is unknown. Here, we show that a Populus class III HD-Zip gene, PtrHB7, was preferentially expressed in cambial zone. PtrHB7-suppressed plants displayed significant changes in vascular tissues with a reduction in xylem but increase in phloem. Transcriptional analysis revealed that genes regulating xylem differentiation were down-regulated, whereas genes regulating phloem differentiation were up-regulated. Correspondingly, PtrHB7 overexpression enhanced differentiation of cambial cells toward xylem cells but inhibited phloem differentiation. PtrHB7 regulation on cambial cell differentiation was associated with its transcript abundance. Together, the results demonstrated that PtrHB7 plays a critical role in controlling a balanced differentiation between secondary xylem and phloem tissues in the process of Populus secondary growth in a dosage-dependent manner.

Preparation of ZSM-5 Coated on Monolithic Interconnected Macroporous Al2O3 Using Cheap n-Butylamine as Template

Using cheap n-butylamine as template, ZSM-5 zeolites have been successfully synthesized and coated on mon- olithic interconnected macroporous Al2O3 by the secondary growth method. The use of cheap n-butylamine could significantly reduce the synthesis cost. Hierarchical monolithic ZSM-5 zeolites were prepared from synthetic mix- tures with different H2O/Na2O or SiO2/Al2O3 ratio. The synthesized samples were characterized by scanning elec- tron microscopy （SEM）, X-ray diffraction （XRD）, Fourier transform infrared spectroscopy （FT-IR） and N2 ad- sorption-desorption. The results show that the hierarchical monolithic zeolites were obtained with cheap n-butylamine template as template. During the hydrothermal reaction process, the morphology of the microme- ter-sized support was well maintained. The irregular crystals were formed in a wide range of the H2O/Na2O or SiO2/Al2O3 ratio of synthetic mixtures and coated on monolithic Al2O3. The relative crystallinity of the zeolites was highest at H2O/Na2O=250 or SiO2/Al2O3= 160. This type of composites exhibited hierarchical porous structures and relatively high specific surface areas.