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Article|01 Sep 2021|OPEN
Downregulated expression of S2-RNase attenuates self-incompatibility in “Guiyou No. 1” pummelo
Jianbing Hu1, Qiang Xu1, Chenchen Liu1, Binghao Liu2, Chongling Deng2, Chuanwu Chen2, Zhuangmin Wei3, Muhammad Husnain Ahmad1, Kang Peng1, Hao Wen1, Xiangling Chen4, Peng Chen5, Robert M. Larkin1, Junli Ye1, Xiuxin Deng1 & Lijun Cha1,
1Key Laboratory of Horticultural Plant Biology, Ministry of Education, College of Horticulture and Forestry Sciences, Huazhong Agricultural University, Wuhan 430070, People’s Republic of China
2Guangxi Engineering Research Center of Citrus Breeding and Culture, Guangxi Academy of Specialty Crops, Guilin 541004, People’s Republic of China
3Guangxi Subtropical Crops Research Institute, Nanning 530001, People’s Republic of China
4Horticulture Research Institute, Guangxi Academy of Agriculture Sciences, Nanning Investigation & Experiment Station of South Subtropical Fruit Trees, Ministry of Agriculture,Nanning 530007 Guangxi, People’s Republic of China
5Horticultural Institute, Hunan Academy of Agricultural Sciences, Changsha 410125, People’s Republic of China

Horticulture Research 8,
Article number: 199 (2021)
doi: 10.1038/hortres.2021.199
Views: 66

Received: 28 Feb 2021
Revised: 27 May 2021
Accepted: 01 Jun 2021
Published online: 01 Sep 2021

Abstract

Self-incompatibility (SI) substantially restricts the yield and quality of citrus. Therefore, breeding and analyzing self-compatible germplasm is of great theoretical and practical significance for citrus. Here, we focus on the mechanism of a self-compatibility mutation in ‘Guiyou No. 1’ pummelo (Citrus maxima), which is a spontaneous mutant of ‘Shatian’ pummelo (Citrus maxima, self-incompatibility). The rate of fruit set and the growth of pollen tubes in the pistil confirmed that a spontaneous mutation in the pistil is responsible for the self-compatibility of ‘Guiyou No. 1’. Segregation ratios of the S genotype in F1 progeny, expression analysis, and western blotting validated that the reduced levels of S2-RNase mRNA contribute to the loss of SI in ‘Guiyou No. 1’. Furthermore, we report a phased assembly of the ‘Guiyou No. 1’ pummelo genome and obtained two complete and well-annotated S haplotypes. Coupled with an analysis of SV variations, methylation levels, and gene expression, we identified a candidate gene (CgHB40), that may influence the regulation of the S2-RNase promoter. Our data provide evidence that a mutation that affects the pistil led to the loss of SI in ‘Guiyou No. 1’ by influencing a poorly understood mechanism that affects transcriptional regulation. This work significantly advances our understanding of the genetic basis of the SI system in citrus and provides information on the regulation of S-RNase genes.