Genome-wide identification of ARID-HMG related genes in citrus and functional analysis of FhARID1 in apomixis and axillary bud development

Polyembryony has posed a significant impediment to the advancement of citrus hybrid breeding. FhRWP is widely regarded as a pivotal factor governing asexual reproduction in citrus, and prior research has demonstrated that FhARID1, acting as an upstream regulator, modulates FhRWP expression. In this study, we performed a genome-wide characterization of the ARID-HMG-related genes using the short juvenile mini-citrus Fortunella hindsii. A total of 20 ARID-HMG-related genes were identified. Protein interaction network and enrichment analysis suggested that ARID-HMG-related proteins might might be involved in chromatin remodeling complexes. Knockout of FhARID1 in F. hindsii did not induce the conversion from polyembryony to monoembryony. However, fharid1 plants in T₁ generation exhibited abnormal proliferation at axillary buds, which is similar to phenotype of fhrwp plants. Expression analysis of fharid1 ovary tissues revealed the downregulation of FhRWP. The results indicated that FhARID1, as an upstream regulator of FhRWP, has an effect on the development of citrus axillary buds. Expression analysis of overexpressed leaves of FhARID1 lines showed that no significant up-regulation of FhRWP, indicating that FhARID1 is not the sole upstream regulatory factor of FhRWP. Only FhARID2 showed a correlation in expression with FhARID1 among the ARID-related genes, further supporting the notion that this gene may be involved in complex formation rather than acting alone. Yeast two-hybrid and MS/MS spectra further indicated that FhARID1 function requires casein kinase II-mediated post-transcriptional phosphorylation. This study elucidated the function of FhARID1 in citrus apomixis and axillary bud development, providing a fundamental basis for understanding the role of ARID-HMG-related genes.