Abstract
BackgroundSugar beet is a highly salt-tolerant crop. However, its ability to withstand high salinity is reduced compared to sea beet, a wild ancestor of all beet crops. The aim of this study was to investigate transcriptional patterns associated with physiological, cytological and biochemical mechanisms involved in salt response in these closely related subspecies. Salt acclimation strategies were assessed in plants subjected to either gradually increasing salt levels (salt-stress) or in excised leaves, exposed instantly to salinity (salt-shock).ResultThe majority of DEGs was down-regulated under stress, which may lead to certain aspects of metabolism being reduced in this treatment, as exemplified by lowered transpiration and photosynthesis. This effect was more pronounced in sugar beet. Additionally, sugar beet, but not sea beet, growth was restricted. Silencing of genes encoding numerous transcription factors and signaling proteins was observed, concomitantly with the up-regulation of lipid transfer protein-encoding genes and those coding for NRTs. Bark storage protein genes were up-regulated in sugar beet to the level observed in unstressed sea beet. Osmotic adjustment, manifested by increased water and proline content, occurred in salt-shocked leaves of both genotypes, due to the concerted activation of genes encoding aquaporins, ion channels and osmoprotectants synthesizing enzymes. bHLH137 was the only TF-encoding gene induced by salt in a dose-dependent manner irrespective of the mode of salt treatment. Moreover, the incidence of bHLH-binding motives in promoter regions of salinity-regulated genes was significantly greater than in non-regulated ones.ConclusionsMaintaining homeostasis under salt stress requires deeper transcriptomic changes in the sugar beet than in the sea beet. In both genotypes salt shock elicits greater transcriptomic changes than stress and it results in greater number of up-regulated genes compared to the latter. NRTs and bark storage protein may play a yet undefined role in salt stress-acclimation in beet. bHLH is a putative regulator of salt response in beet leaves and a promising candidate for further studies.
Highlights
Sugar beet is a highly salt-tolerant crop
NRTs and bark storage protein may play a yet undefined role in salt stress-acclimation in beet. Basic helixloop-helix proteins (bHLH) is a putative regulator of salt response in beet leaves and a promising candidate for further studies
The aim of this study was to compare transcriptional changes associated with physiological, cytological and biochemical mechanisms involved in salt response elicited by two modes of treatment in two beet subspecies differing in salt tolerance
Summary
Its ability to withstand high salinity is reduced compared to sea beet, a wild ancestor of all beet crops. Taking into account the difference in salt tolerance between sugar beet and its wild relative, the possibility arises to identify the salt tolerance mechanisms which were lost during domestication. This goal can be achieved by comparing salt acclimation strategies in plants representing both genotypes. To date, such type of studies was performed mainly on tomato. They involved cultivars of Solanum lycopersicum and wild species such as S. peruvianum and S. pimpinellifolium [10, 11]
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