PpMYB36 Encodes a MYB-Type Transcription Factor That Is Involved in Russet Skin Coloration in Pear (Pyrus pyrifolia)

Abstract

Fruit color is one of the most important external qualities of pear (Pyrus pyrifolia) fruits. However, the mechanisms that control russet skin coloration in pear have not been well characterized. Here, we explored the molecular mechanisms that determine the russet skin trait in pear using the F1 population derived from a cross between russet skin (‘Niitaka’) and non-russet skin (‘Dangshansu’) cultivars. Pigment measurements indicated that the lignin content in the skin of the russet pear fruits was greater than that in the non-russet pear skin. Genetic analysis revealed that the phenotype of the russet skin pear is associated with an allele of the PpRus gene. Using bulked segregant analysis combined with the genome sequencing (BSA-seq), we identified two simple sequence repeat (SSR) marker loci linked with the russet-colored skin trait in pear. Linkage analysis showed that the PpRus locus maps to the scaffold NW_008988489.1: 53297-211921 on chromosome 8 in the pear genome. In the mapped region, the expression level of LOC103929640 was significantly increased in the russet skin pear and showed a correlation with the increase of lignin content during the ripening period. Genotyping results demonstrated that LOC103929640 encoding the transcription factor MYB36 is the causal gene for the russet skin trait in pear. Particularly, a W-box insertion at the PpMYB36 promoter of russet skin pears is essential for PpMYB36-mediated regulation of lignin accumulation and russet coloration in pear. Overall, these results show that PpMYB36 is involved in the regulation of russet skin trait in pear.

Transcriptome and metabolome analyses reveal phenotype formation differences between russet and non-russet apples

“…In plants, various MYB transcription factors regulate either suberin biosynthesis or extracellular lipid accumulation. In pears, 12 MYB genes involved in plant tissue suberization were differentially upregulated in the russet fruit skin, indicating that these MYB genes may affect russeting formation by regulating suberin synthesis ( Ma et al., 2021 ). In addition, MYB9 and MYB107 ( Lashbrooke et al., 2016 ), MYB6 and MYB67 ( Falginella et al., 2021 ), and MYB93 ( Legay et al., 2016 ) involvement has been reported in suberin in fruit russeting.…”

“…The main effector gene controlling russet variation in ‘Renetta Grigia di Torriana’ apples is located on chromosome LG12 ( Falginella et al., 2015 ). The PpRus gene, which controls the pear russet skin trait, was identified via Bulked Segregant analysis and is located on chromosome 8 of the pear genome ( Ma et al., 2021 ).…”

Advances in Understanding the Causes, Molecular Mechanism, and Perspectives of Russeting on Tree Fruit

“…QTL analysis of this population showed that russeting loci were located on Chr 3, 19, and 23 ( Macnee et al, 2021 ). In a recent study, BSA-seq (RNA-seq-based bulked segregant analysis) was performed, in which linkage analysis found that the PpRus locus is located on Chr 8 ( Ma et al, 2021 ). As these results indicate that hybrid groups are appropriate materials to study russeting in fruit tree, they may provide more unique phenotypes for further study.…”

“…In pear, transient expression of PbHHT1 gene in young green non-russet fruits led to a lenticel suberization genotype with higher content of ω-feruloyloxypalmitic acid ( Shi et al, 2021 ). Using BSA-seq, a MYB transcription factor MYB36 was identified as a regulator that was involved in lignin accumulation and russet coloration in pear ( Ma et al, 2021 ). In addition to the above genes, ABCGs were also involved in suberin formation and fruit russeting ( Falginella et al, 2015 ; Hou et al, 2018 ; Shi et al, 2021 ), but the functions of this family remain to be determined in fruit tree.…”

“…Methods to prevent russeting include bagging, using phytohormones (e.g., BA and GA), and other measures ( Alston and Watkins, 1973 ; Heng et al, 2016 ; Wang et al, 2021 ). Research on russeting mainly involved studying the suberin, cutin layer, and lignin biosynthetic pathway ( Lashbrooke et al, 2016 ; Wang et al, 2020 ; Ma et al, 2021 ; Shi et al, 2021 ). Although a review of the molecular research of russet/semi-russet of sand pear was reported previously ( Wang et al, 2016 ), the molecular research of russeting in tree fruit has not been discussed till now.…”