Goto Shingo, Fujii Hiroshi, Hamada Hiroko, Ohta Satoshi, Endo Tomoko, Shimizu Tokurou, Nonaka Keisuke, Shimada Takehiko
Citrus Breeding and Production Group, Division of Citrus Research, Institute of Fruit Tree and Tea Science, National Agriculture and Food Research Organization (NARO), Shizuoka, Japan.
Front Plant Sci. 2023 Jun 5;14:1163358. doi: 10.3389/fpls.2023.1163358. eCollection 2023.
In citrus breeding programs, male sterility is an important trait for developing seedless varieties. Sterility associated with the male sterile cytoplasm of Kishu mandarin (Kishu-cytoplasm) has been proposed to fit the cytoplasmic male sterility (CMS) model. However, it remains undetermined whether CMS in citrus is controlled by interactions between sterile cytoplasm and nuclear restorer-of-fertility () genes. Accordingly, mechanisms underlying the control of the wide phenotypic variation in pollen number for breeding germplasm should be elucidated. This study aimed to identify complete linkage DNA markers responsible for male sterility at the region based on fine mapping. Two P-class pentatricopeptide repeat (PPR) family genes were identified as candidates for based on predicted mitochondrial localization and higher expression in a male fertile variety/selected strain than in a male sterile variety. Eleven haplotypes (HT1-HT11) at the region were defined based on genotyping of DNA markers. Association analysis of diplotypes at the region and the number of pollen grains per anther (NPG) in breeding germplasms harboring Kishu-cytoplasm revealed that the diplotypes in this region influenced NPG. Among these haplotypes, HT1 is a non-functional restorer-of-fertility () haplotype; HT2, a less-functional ; HT3-HT5 are semi-functional ; and HT6 and HT7 are functional . However, the rare haplotypes HT8-HT11 could not be characterized. Therefore, P-class PPR family genes in the region may constitute the nuclear genes within the CMS model, and a combination of the seven haplotypes could contribute to phenotypic variation in the NPG of breeding germplasms. These findings reveal the genomic mechanisms of CMS in citrus and will contribute to seedless citrus breeding programs by selecting candidate seedless seedlings using the DNA markers at the region.
在柑橘育种计划中，雄性不育是培育无核品种的一个重要性状。与纪州蜜柑雄性不育细胞质（纪州细胞质）相关的不育现象被认为符合细胞质雄性不育（CMS）模型。然而，柑橘中的CMS是否由不育细胞质与核育性恢复基因（Rf）之间的相互作用所控制仍未确定。因此，应阐明控制育种种质花粉数量广泛表型变异的潜在机制。本研究旨在通过精细定位确定负责该区域雄性不育的完全连锁DNA标记。基于预测的线粒体定位以及在雄性可育品种/选定品系中比在雄性不育品种中更高的表达，鉴定出两个P类五肽重复（PPR）家族基因作为Rf的候选基因。基于DNA标记的基因分型，确定了该区域的11种单倍型（HT1-HT11）。对含有纪州细胞质的育种种质中该区域的双倍型与每花药花粉粒数（NPG）进行关联分析，结果表明该区域的双倍型影响NPG。在这些单倍型中，HT1是一个无功能的育性恢复（Rf）单倍型；HT2，功能较弱；HT3-HT5是半功能的Rf；HT6和HT7是功能型的Rf。然而，罕见单倍型HT8-HT11的特征尚不明确。因此，该区域的P类PPR家族基因可能构成CMS模型中的核Rf基因，这七种单倍型的组合可能导致育种种质NPG的表型变异。这些发现揭示了柑橘中CMS的基因组机制，并将通过使用该区域的DNA标记选择候选无核幼苗，为无核柑橘育种计划做出贡献。
