Diel pattern of circadian clock and storage protein gene expression in leaves and during seed filling in cowpea (Vigna unguiculata)

Abstract

BackgroundCowpea (Vigna unguiculata) is an important source of protein supply for animal and human nutrition. The major storage globulins VICILIN and LEGUMIN (LEG) are synthesized from several genes including LEGA, LEGB, LEGJ and CVC (CONVICILIN). The current hypothesis is that the plant circadian core clock genes are conserved in a wide array of species and that primary metabolism is to a large extent controlled by the plant circadian clock. Our aim was to investigate a possible link between gene expression of storage proteins and the circadian clock.ResultsWe identified cowpea orthologues of the core clock genes VunLHY, VunTOC1, VunGI and VunELF3, the protein storage genes VunLEG, VunLEGJ, and VunCVC as well as nine candidate reference genes used in RT-PCR. ELONGATION FACTOR 1-A (ELF1A) resulted the most suitable reference gene. The clock genes VunELF3, VunGI, VunTOC1 and VunLHY showed a rhythmic expression profile in leaves with a typical evening/night and morning/midday phased expression. The diel patterns were not completely robust and only VungGI and VungELF3 retained a rhythmic pattern under free running conditions of darkness. Under field conditions, rhythmicity and phasing apparently faded during early pod and seed development and was regained in ripening pods for VunTOC1 and VunLHY. Mature seeds showed a rhythmic expression of VunGI resembling leaf tissue under controlled growth chamber conditions. Comparing time windows during developmental stages we found that VunCVC and VunLEG were significantly down regulated during the night in mature pods as compared to intermediate ripe pods, while changes in seeds were non-significant due to high variance. The rhythmic expression under field conditions was lost under growth chamber conditions.ConclusionsThe core clock gene network is conserved in cowpea leaves showing a robust diel expression pattern except VunELF3 under growth chamber conditions. There appears to be a clock transcriptional reprogramming in pods and seeds compared to leaves. Storage protein deposition may be circadian regulated under field conditions but the strong environmental signals are not met under artificial growth conditions. Diel expression pattern in field conditions may result in better usage of energy for protein storage.Electronic supplementary materialThe online version of this article (10.1186/s12870-018-1244-2) contains supplementary material, which is available to authorized users.

The clock gene Gigantea 1 from Petunia hybrida coordinates vegetative growth and inflorescence architecture

“…1f). Peak expression towards the end of the day was also reported for Arabidopsis 51 , soybean 16 or cowpea 17 . In our case, the expression pattern in iRNA::PhGI1 lines was similar to wildtype plants however, peak expression was advanced by three hours in all three transgenic silenced lines (Fig.…”

“…This pattern is similar to that observed in Arabidopsis, were under long day conditions (16:8 LD), GI mRNA peaks at ZT 10 and lowest expression www.nature.com/scientificreports www.nature.com/scientificreports/ levels occur at ZT 0 30 . Other examples of an evening phased expression pattern for GI include cowpea 17,52 and soybean 16 . In Arabidopsis, CCA1 binds to the G1 promoter and reduces its expression, which only rises towards midday, when CCA1 expression is repressed by TOC1 53 .…”

“…www.nature.com/scientificreports www.nature.com/scientificreports/ stress response 16 , the expression of seed storage proteins 17 , biomass production [18][19][20] , flower orientation 19 and flower scent emission [21][22][23][24] .…”

Molecular and transcriptional structure of the petal and leaf circadian clock inPetunia hybrida

“…It defines the timing of floral scent emission in a variety of plants including Petunia or Nicotiana attenuatta (Fenske et al , 2015; Yon et al , 2015; Terry et al , 2019). The plant circadian clock appears to have a specific transcriptional structure in different tissues such as leaves, pods, seeds, or roots (Thain et al , 2002; James et al , 2008; Bordage et al , 2016; Weiss et al , 2018). As the transcriptional structure of the clock in petal is currently unknown, we used Petunia hybrida to perform a detailed analysis.…”

Evaluating stress responses in cowpea under drought stress

“…upregulated in drought-tolerant cultivars from different crops under water deficit conditions (Sato and Yokoya, 2008;Temel et al, 2017). For comparison, VuEF1-α and VuPp2A genes were selected as reference genes due to their stability under drought stress conditions (Da Silva et al, 2015;Weiss et al, 2018). Gene expression analysis by qPCR revealed that both DG genes were mostly expressed at 25% and 0% of FC treatments (Fig.…”