The expression of a candidate cucumber fruit sugar starvation marker gene CsSEF1 is enhanced in malformed fruit induced by salinity

Abstract

The cucumber ( L.) gene () was suggested to be a good marker gene for sugar starvation in fruit. The expression of this gene in fruits is dramatically upregulated in plants that have suffered either complete defoliation or prolonged darkness. was initially discovered as a gene that was upregulated during somatic embryogenesis. We examined the difference in fruit parts and the effect of pollination on the upregulation of induced by defoliation treatment. The results indicated that the upregulation of in fruit by defoliation is not dependent on the presence of developing embryos. The expression of was upregulated in malformed fruit induced by salinity in which the development of placenta was arrested. Partial cutting of the distal part of the fruit showed that if placenta tissue remained there was no upregulation of , whereas when placenta tissue did not remain there was a marked upregulation of. These results could be consistently interpreted as showing that placenta tissue induced the transport of photoassimilates to the fruit and that without developing placenta tissue, pericarp tissue suffers from severe sugar starvation. This interpretation, in turn, enforces the view that is a good marker gene of fruit sugar starvation.

Expression of Candidate Marker Genes of Sugar Starvation is Enhanced in Growth-Suppressed Parthenocarpic Cucumber Fruit

“…The variation of the data was much larger than that reported previously (Tazuke and Asayama 2013; Tazuke et al 2015; Tazuke et al 2017). The study of the effect of salinity on fruit growth revealed that the RGR of a fruit in which growth was suppressed by salinity tended to fall to about 1.5% h -1 (Tazuke 1997).…”

“…In our previous studies, the expression of the AS, CsSEF1, and CsFDI1 genes in young fruit increased similarly in response to total defoliation, prolonged darkness, salinity, and fruit harvest (Tazuke et al 2015;Tazuke et al 2017;Tazuke and Kinoshita 2018). This correlation could explain the di culty in delineating the causes of gene expression, such as sugar starvation and growth cessation.…”

Expression of candidate marker genes of sugar starvation is upregulated in growth-suppressed parthenocarpic cucumber fruit. Novel gene markers for sugar starvation in growth-suppressed cucumber fruit

“…In these three genes, the upregulation of the genes was mainly seen on 6 DAA. Because the expression of these three genes was tested in many experiments (Tazuke and Asayama, 2013;Tazuke et al, 2015;Tazuke et al, 2017;Tazuke and Kinoshita, 2018;Tazuke et al, 2019), it is highly likely that they are good markers of sugar starvation, although the gene function is known only in AS. Thus, in fruits whose RGR became close to zero, it is most probable that severe sugar starvation is occurring.…”

“…The upregulation of candidate sugar starvation genes together with the reduction of hexose concentration close to zero strongly suggests that the candidate genes are genuine sugar starvation markers. In an experiment removing the ovary, it was suggested that stopping of sugar import (loss of sink activity) together with the remaining growth activity causes sugar starvation (Tazuke et al, 2017). Thus, loss of sink activity may occur in slow growing fruits, and it is possible to hypothesize that sugar starvation caused by loss of sink activity triggers fruit abortion.…”

“…The function of the remaining two genes remains unclear. However, the expression of Cucumis sativus putative CCCH-type zinc finger protein CsSEF1 (CsSEF1) and C. sativus BTB/POZ domain-containing protein At1g63850-like (CsFDI1) was markedly upregulated by total defoliation (Tazuke and Asayama, 2013;Tazuke et al, 2015), prolonged darkness (Tazuke and Asayama, 2013;Tazuke et al, 2015), salinity (Tazuke et al, 2017), removal of the ovary (Tazuke et al, 2017), and fruit harvest (Tazuke and Kinoshita, 2018), strongly suggesting that these genes are good markers of sugar starvation. In a preliminary experiment, the growth cessation of parthenocarpic cucumber fruit was accompanied by upregulation of the AS, CsSEF1, and CsFDI1 genes, suggesting the occurrence of sugar starvation during growth cessation or abortion of a fruit (Tazuke, unpublished data).…”