Nodulin 26-like intrinsic proteins (NIPs) are a family of channel-forming transmembrane proteins that function in the transport of water and other small molecules.  Some NIPs can mediate silicon transport across plasma membranes and lead to silicon accumulation in plants, which is beneficial for the growth and development of plants.  Cucumber is one of the most widely consumed vegetables; however, the functions of NIPs in this crop are still largely unknown.  Here, we report the functional characteristics of CsNIP2;2.  It was found that CsNIP2;2 is a tandem repeat of CsNIP2;1, which had been demonstrated to be a silicon influx transporter gene.  CsNIP2;2 has a selectivity filter composed of cysteine, serine, glycine and arginine (CSGR), which is different from all previously characterized silicon influx transporters in higher plants at the second helix position.  Xenopus laevis oocytes injected with CsNIP2;2 cRNA demonstrated a higher uptake of silicon than the control, and the uptake remained unchanged under low temperature.  CsNIP2;2 was found to be expressed in the root, stem, lamina and petiole, and exogenous silicon treatment decreased its expression in the stem but not in other tissues.  Transient expression of CsNIP2;2-eGFP fusion sequence in onion epidermal cells showed that CsNIP2;2 was localized to the cell nucleus, plasma membrane and an unknown structure inside the cell.  The results suggest that CsNIP2;2 is a silicon influx transporter in cucumber, and its subcellular localization and the selectivity filter are different from those of the previously characterized silicon influx transporters in other plants.  These findings may be helpful for understanding the functions of NIPs in cucumber plants.

Tomato (Solanum lycopersicum) is a model plant for research on fruit development and stress response, in which gene expression analysis is frequently conducted.  Quantitative PCR (qPCR) is a widely used technique for gene expression analysis, and the selection of reference genes may affect the accuracy of results and even conclusions.  Although there have been some frequently used reference genes in tomato, it has been shown that the expressions of some of these genes are not constant in different tissues and environmental conditions.  Moreover, little information on genomic identification of reference genes is available in tomato.  Here, we mined the publicly available transcriptional sequencing data and screened out fifteen candidate reference genes, and the expression stability of these candidate genes and seven traditionally used ones were evaluated under stress and hormone treatment.  The results showed that over half of the selected candidate references were housekeeping genes in tomato cells.  Among the candidate reference genes and the traditionally used ones, the most stably expressed genes varied under different treatments, and most of these genes were recommended as preferred reference genes at least once except Solyc04g009030 and Solyc07g066610, two traditionally used reference genes.  This study provides some novel reference genes in tomato, and the preferred reference genes under different environmental stimuli, which may be useful for future research.  Our study suggests that excavating stably expressed genes from transcriptome sequencing data is a reliable approach to screening reference genes for qPCR analysis.