Nucleo-cytoplasmic interaction in seedless cybrid citrus

The mitochondrial genome of cybrid citrus (G1 + HBP) is from the CMS callus parent ‘Guoqing No. 1’ Satsuma mandarin (G1), while the nuclear and chloroplast genomes of G1 + HBP are from the fertile mesophyll parent Hirado Buntan pummelo (HBP). The tree of G1+HBP resembles HBP, as well as fruit appearance and flavor, while G1+HBP showed typical male sterility including degenerated petals and stamens and aborted pollen which resulted in seedless fruit. The interaction of mitochondrion from CMS parent G1and nucleus from HBP might attribute to male sterility of G1+HBP. The male sterility candidate genes of the cybrid were identified using comparation analysis of omics and mitochondrial genome, while the interaction pattern of mitochondrion and nuclear in this cybrid is still unknown.

This article has been published on Horticulture Research with title: Spatiotemporal profiles of gene activity in stamen delineate nucleo-cytoplasmic interaction in a male-sterile somatic cybrid citrus.

In this study, stamen organ and cell types at five important stages were confirmed by morphology observation and collected using laser microdissection. The spatiotemporal expression of genes in stamen of citrus were profiled by RNA-Seq.

This study identified differentially expressed genes (DEGs) related to stamen development in stamen primordia, meiocytes and microspores of G1+HBP. ABCE model genes were systematically analyzed, and B class gene CgAP3.2, a newly identified AP3 homologous in citrus, was selected as the candidate gene involved in stamen development, according to gene expression and protein interaction assay. The dysfunction of mitochondria in G1+HBP was elucidated, and nucleo-cytoplasmic interactions were proposed based on GO enrichment analysis of DEGs, measurement of hormones and primary metabolism content of flower bud. In stamen primordia of G1+HBP, the jasmonic acid (JA) and auxin (IAA) metabolism were disrupted. In addition, the expression pattern of DEGs related to JA metabolism pathway, photosynthesis and tricarboxylic acid cycle (TCA) was consistent. The exogenous mitochondrion might disrupt IAA metabolism directly, and affect JA metabolism indirectly through the abnormal photosynthesis in chloroplasts, which together changed the expression of stamen primordia development related genes. Respiration and mitochondria related cellular components were disrupted in meiocytes of G1+HBP, and mitochondrial nucleobase metabolism were disrupted in microspores of G1+HBP, which together indicated that the dysfunction of mitochondria might affect meiosis and microspores development and resulted in pollen abortion. This study proposed potential nucleo-cytoplasmic interaction network in stamen of citrus, which supports mechanisms disclosure of cytoplasmic male sterility in citrus.

This research was supported by National Key Laboratory for Germplasm Innovation & Utilization of Horticultural Crops and Hubei Hongshan Laboratory, and financially supported by the Ministry of Science and Technology of China (2022YFF1003101), the National Natural Science Foundation of China (31530065, 31820103011, 32202451), and the Foundation of Hubei Hongshan Laboratory (2021hszd009).

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References

Authors

Nan Jiang, Meng-Qi Feng, Lai-Chao Cheng, Li-Hua Kuang, Chao-Chao Li, Zhao-Ping Yin, Rong Wang, Kai-Dong Xie, Wen-Wu Guo, Xiao-Meng Wu*

Affiliations

Huazhong Agricultural University

About the Wenwu Guo lab in National Key Laboratory for Germplasm Innovation & Utilization of Horticultural Crops in Huazhong Agricultural University (HZAU)

Dr. Wenwu Guo, professor of National Key Laboratory for Germplasm Innovation & Utilization of Horticultural Crops in Huazhong Agricultural University (HZAU), his research group is engaged in citrus cell engineering and genetic improvement. The group focuses on improving the breeding efficiency of citrus and breeding new varieties with seedless fruit, high resistance, wide adaptation and high quality via cell engineering approaches. Dr. Guo proposed a new strategy to breed seedless cybrid citrus via somatic cell fusion, which shortened the breeding cycle for at least 20 years compared with 6-7 generations of backcrossing. Dr. Guo’s group also produced numerous polyploid citrus germplasm resources for seedless breeding, and devotes to reveal the mechanisms of male sterility, somatic embryogenesis, and epigenetic variations underlying wide adaptability of polyploid citrus.