A Combined Metabolome and Transcriptome Reveals the Lignin Metabolic Pathway during the Developmental Stages of Peel Coloration in the 'Xinyu' Pear.

Sand pear is the main cultivated pear species in China, and brown peel is a unique feature of sand pear. The formation of brown peel is related to the activity of the cork layer, of which lignin is an important component. The formation of brown peel is intimately associated with the biosynthesis and accumulation of lignin; however, the regulatory mechanism of lignin biosynthesis in pear peel remains unclear. In this study, we used a newly bred sand pear cultivar 'Xinyu' as the material to investigate the biosynthesis and accumulation of lignin at nine developmental stages using metabolomic and transcriptomic methods. Our results showed that the 30 days after flowering (DAF) to 50DAF were the key periods of lignin accumulation according to data analysis from the assays of lignin measurement, scanning electron microscope (SEM) observation, metabolomics, and transcriptomics. Through weighted gene co-expression network analysis (WGCNA), positively correlated modules with lignin were identified. A total of nine difference lignin components were identified and 148 differentially expressed genes (DEGs), including 10 structural genes (PAL1, C4H, two 4CL genes, HCT, CSE, two COMT genes, and two CCR genes) and MYB, NAC, ERF, and TCP transcription factor genes were involved in lignin metabolism. An analysis of RT-qPCR confirmed that these DEGs were involved in the biosynthesis and regulation of lignin. These findings further help us understand the mechanisms of lignin biosynthesis and provide a theoretical basis for peel color control and quality improvement in pear breeding and cultivation.

Genome-Wide Identification and Expression Profiling Analysis of SWEET Family Genes Involved in Fruit Development in Plum (Prunus salicina Lindl).

SWEETs (sugars will eventually be exported transporters) play a vital role in longer-distance sugar transportation, and thus control carbon flow and energy metabolism in plants. SWEET genes have been identified in various plant species, but their functions in fruit development remain uncharacterized. Here, we isolated 15 putative PsSWEETs from the Prunus salicina genome. For further analysis, comprehensive bioinformatics methods were applied to determine the gene structure, chromosome distribution, phylogeny, cis-acting regulatory elements, and expression profiles of PsSWEETs. qRT-PCR analysis suggested that these SWEETs might have diverse functions in the development of plum fruit. The relative expression levels of PsSWEET1 and PsSWEET9 were obviously higher in ripened fruit than the ones in other developmental stages, suggesting their possible roles in the transport and accumulation of sugars in plum fruit. Positive correlations were found between the expression level of PsSWEET3/10/13 and the content of sucrose, and the expression level of PsSWEET2 and the content of fructose, respectively, during the development of 'Furongli' fruit, suggesting their possible roles in the accumulation of sucrose and fructose. The current study investigated the initial genomic characterization and expression patterns of the SWEET gene family in plum, which could provide a foundation for the further understanding of the functional analysis of the SWEET gene family.

Organic amendments alleviate early defoliation and increase fruit yield by altering assembly patterns and of microbial communities and enzymatic activities in sandy pear (Pyrus pyrifolia).

Severe early defoliation has become an important factor restricting the development of the pear industry in southern China. However, the assembly patterns of microbial communities and their functional activities in response to the application of bioorganic fertilizer (BIO) or humic acid (HA) in southern China's pear orchards remain poorly understood, particularly the impact on the early defoliation of the trees. We conducted a 3-year field experiment (2017-2019) in an 18-year-old 'Cuiguan' pear orchard. Four fertilization schemes were tested: local custom fertilization as control (CK), CK plus HA (CK-HA), BIO, and BIO plus HA (BIO-HA). Results showed that BIO and BIO-HA application decreased the early defoliation rate by 50-60%, and increased pear yield by 40% compared with the CK and CK-HA treatments. The BIO and BIO-HA application significantly improved soil pH, available nutrient content, total enzyme activity and ecosystem multifunctionality, and also changed the structure of soil bacterial and fungal communities. The genus Acidothermus was positively correlated with the early defoliation rate, while the genus Rhodanobacter was negatively correlated. Additionally, random forest models revealed that the early defoliation rate could be best explained by soil pH, ammonium content, available phosphorus, and total enzyme activity. In conclusion, application of BIO or BIO mixed with HA could have assembled distinct microbial communities and increased total enzyme activity, leading to significant improvement of soil physicochemical traits. The increased availability of soil nutrient thus changed leaf nutrient concentrations and alleviated the early defoliation rate of pear trees in acid red soil in southern China.