In the Nicotiana tabacum flower development study, we identified SCI1 (Stigma/style Cell-cycle Inhibitor 1), a regulator of cell proliferation. SCI1 interacts with NtCDKG;2 (N. tabacum Cyclin-Dependent Kinase G;2), a homolog of human CDK11, which is responsible for RanGTP-dependent microtubule stabilization, regulating spindle assembly rate. In a Y2H screening of a cDNA library using NtCDKG;2 as bait, a RanBP1 (Ran-Binding Protein 1) was revealed as its interaction partner. RanBP1 is an essential regulatory protein of the RanGTPase system, contributing to the formation of the Ran gradient, which modulates different important cellular processes. RanBP1 is crucial in the nuclear import/export machinery during interphase and spindle checkpoint formation during cell division. These processes are well studied in animals, but very little is known about them in plants. We confirmed NtCDKG;2 and NtRanBP1 interaction by pairwise Y2H and characterized the localization of both proteins during plant cell division. We demonstrated the presence of NtRanBP1 in the cytoplasm during interphase and its nuclear arrest at mitosis onset. Meanwhile, we showed that NtCDKG;2 is localized in the mitotic spindle during cell division, indicating an analogous function to the human CDK11. We propose that the phosphorylation of the nuclear export signal at RanBP1 by NtCDKG;2 may be responsible for the reported nuclear arrest.

Sugarcane and energy cane (Saccharum spp. hybrids) yields are significantly threatened by smut disease, caused by the fungus Sporisorium scitamineum. Gene expression studies are essential for understanding molecular responses in this pathosystem; however, reference gene stability may vary among genotypes, plant organs, and across infection stages, highlighting the need for systematic validation under the specific conditions of each experiment. In this study, eight candidate genes were assessed in the buds of sugarcane IACSP02-1064 (intermediate resistance) and energy cane Vertix 10 (susceptible) during the course of the infection (12, 24, 48, and 120 hpi). Expression stability was assessed using geNorm, NormFinder, and BestKeeper algorithms. For IACSP02-1064, ACAD (Acyl-CoA dehydrogenase family member 10) and GAPDH (Glyceraldehyde-3-phosphate dehydrogenase) were the most stable genes, whereas GAPDH/ACAD and ACAD/UBQ2 (Ubiquitin 2) were identified as optimal pairs. For Vertix 10, GAPDH, UBQ2, and ACAD showed the highest stability, while GAPDH/UBQ2, ACAD/GAPDH, and ACAD/SARMp1 were recommended for normalization. The selected reference genes were further evaluated by analyzing ScSPL19 (SQUAMOSA promoter-binding protein-like 19 from Saccharum spp.) expression, a member of the SQUAMOSA PROMOTER-BINDING PROTEIN-LIKE (SPL) transcription factor family, whose members have previously been reported to respond to smut infection, using the most and least stable reference gene pairs. This analysis revealed differential temporal regulation of ScSPL19 when normalized with the most stable reference gene pair (GAPDH/ACAD). These results support the suitability of this reference gene combination for accurate relative gene expression analysis under the evaluated conditions.