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Loess is a kind of special sediment with pore structure and rich carbonate in its composition. Due to the characteristics of structure and composition, most loess has collapsibility. There are rich loess resources distributed in the northwest area of China. With the improvement of the traffic network in the west area, the use of loess as roadbed is gradually increasing. Therefore, during the construction process, the engineering problems encountered by loess also increased, which seriously hindered the construction process of the traffic network. Most of loess in our country is collapsible loess. So the common problem in engineering is how to dispose the collapsibility of collapsible loess.In this paper, the characteristics and evaluation indexes of loess are summarized and studied, the mechanism of loess collapsibility is further explored, and the three methods of loess collapsibility treatment are summarized, which will provide guidance for future engineering problems in collapsible loess areas.

Osmanthus fragrans 'Yinbi Shuanghui' is a colored leaf variety of O. fragrans. To study the mechanism of leaf color formation in O. fragrans 'Yinbi Shuanghui', we selected green and colored leaves with two different parts, namely yellow and green, as our research materials. We analyzed the expression changes related to leaf color in genes by performing qRT-PCR in the different leaf parts, finding that OfPAO was significantly up-regulated in the yellow part of colored leaves, and we initially determined that OfPAO was the key gene involved in the formation of colored leaves. Then, we constructed an OfPAO overexpression vector, before transforming it into tobacco through an Agrobacterium-mediated transformation to obtain transgenic plants. We found that the transgenic tobacco leaf color of OfPAO was lighter than that of the null carrier, the chlorophyll content in leaves decreased, and the expression of genes involved in the chlorophyll degradation pathway in OfPAO transgenic tobacco was up-regulated, suggesting that OfPAO regulates chlorophyll degradation, leading to changes in leaf color. According to the results of transcriptome sequencing and the genome data of O. fragrans 'Rixianggui', we cloned CDS and the promoter sequence of OfPAO, and the promoter regions 901-1307 of the OfPAO were sequenced through bisulfite genomic sequencing PCR (BSP), finding that the methylation level of CHH in the yellow part of colored leaves was lowest in colored and green leaves at 145 bp. The methylation of CHH in the promoter of OfPAO in O. fragrans 'Yinbi Shuanghui' was negatively correlated with the gene expression level, suggesting that the methylation of the promoter of OfPAO may regulate the expression of OfPAO, affecting chlorophyll degradation in the leaves. [ABSTRACT FROM AUTHOR]