Flowering in sugarcane-insights from the grasses

Abstract

Flowering is a crucial phase for angiosperms to continue their species propagation and is highly regulated. In the current review, flowering in sugarcane and the associated mechanisms are elaborately presented. In sugarcane, flowering has two effects, wherein it is a beneficial factor from the breeder's perspective and crucial for crop improvement, but commercially, it depletes the sucrose reserves from the stalks; hence, less value is assigned. Different species of Saccharum genus are spread across geographical latitudes, thereby proving their ability to grow in multiple inductive daylengths of different locations according in the habituated zone. In general, sugarcane is termed an intermediate daylength plant with quantitative short-day behaviour as it requires reduction in daylength from 12 h 55 min to 12 h or 12 h 30 min. The prime concern in sugarcane flowering is its erratic flowering nature. The transition to reproductive stage which reverts to vegetative stage if there is any deviation from ambient temperature and light is also an issue. Spatial and temporal gene expression patterns during vegetative to reproductive stage transition and after reverting to vegetative state could possibly reveal how the genetic circuits are being governed. This review will also shed a light on potential roles of genes and/or miRNAs in flowering in sugarcane. Knowledge of transcriptomic background of circadian, photoperiod, and gibberellin pathways in sugarcane will enable us to better understand of variable response in floral development.

Keywords: Biochemical; Circadian; Flowering; Molecular; Sugarcane; miRNAs.

Fig. 1

Genes [PIF3 (PHYTOCHROME INTERACTING FACTOR3), CCA1 (CIRCADIAN CLOCK ASSOCIATED1)/LHY (LATE ELONGATED HYPOCOTYL), TOC1 (TIMING OF CAB EXPRESSION1), GI (GIGANTEA)] involved in regulating the Circadian clock in Arabidopsis

Fig.2

Flowering gene regulation during day time. (a) Morning time (transcriptional activation of CDFs due to absence of repressors GI & FKF1, Transcriptional inactivation of CO due to repressors CDFs), (b) Transcriptional activation PRRs, Transcriptional inactivation of CDFs by PRRs, and promotion of CO transcription through degradation of CDFs. (c) Afternoon (Blue light activated FKF1 forms complex with GI)

Fig.3

Effect of different lights on flowering genes (a) CO protein destabilized under red-light, (b) CO protein stabilized under far-red & blue light, (c) CRY2- COP1-SPA1 complex releases the CO protein from degradation, (d) Regulation CO transcription and CO degradation at night/dark phase

Fig.4

Transcription activation of miR156 (expression is strongest during the early seedling, juvenile phase, low expression of SPLs (SQUAMOSA PROMOTER BINDING LIKEs), and AP2 upregulates the expression of miR156) and miR172 (expression is low during the juvenile phase and then increases in due course of flowering stage with high expression of SPLs and AP2 downregulates the expression of miR172)

Fig. 5

Photoperiod dependent activation of SPLs and targets of SPLs (CO mediated transcription of FT, forms complex with FD and this FT-FD complex activates the SPL3, SPL4, and SPL5 expression)

Fig. 6

Classification of Plant PEBPs based on the phylogenetic trees constructed (Chardon and Damerval ; Karlgren et al. ; Venail et al. ; Wolabu et al. 2016) At- Arabidopsis thaliana, Sb-Sorghum bicolor, Zcn- Maize, Sc-Sugarcane, Os-Oryza sativa, Hv- Hordeum vulgare, Ta-Triticum aestivum

Fig. 7

Multiple sequence alignment of PEBPs identified in Arabidopsis, Sorghum and Sugarcane showing the conserved and variations in amino acids at a specific position 132 (https://bioedit.software.informer.com/)