Transcript and metabolite signature of maize source leaves suggests a link between transitory starch to sucrose balance and the autonomous floral transition

Abstract

Little is known about the nature of floral inductive cues in day-neutral plants that are insensitive to photoperiod variations and, therefore, rely on endogenous signals to initiate reproductive growth. The INDETERMINATE1 (ID1) transcription factor is a key regulator of the transition to flowering in day-neutral maize. The ID1 gene is expressed exclusively in developing leaves, where it controls the production or transmission of leaf-derived florigenic signals. Florigen-producing source leaves were compared with mature leaves of late-flowering id1 plants, and metabolite and gene expression differences associated with the floral transition in maize were observed. While id1 mutants have a similar capacity for photosynthesis to wild-type siblings, id1 source leaves show quantitative differences in carbohydrate allocation prior to the floral transition stage, with a marked increase in sucrose and other soluble sugars, accompanied by a decrease in tricarboxylic acid (TCA) cycle organic acids. Importantly, source leaves of autonomous-flowering maize are typified by a higher transitory starch to sucrose ratio and a transcript profile enriched for sucrose synthesis and starch metabolism-related gene function. Finally, similar changes in transitory starch and sucrose are not observed in teosinte, the tropical progenitor of maize that requires short-day photoperiods to induce flowering. Together, these data define a transcript and metabolite signature associated with the autonomous floral transition in temperate maize leaves.

Flowering Time-Regulated Genes in Maize Include the Transcription Factor ZmMADS1

“…Differences in their expression during the floral transition in various maize lines indicate that the gene regulatory network controlling FTi in maize is very complex and not universal in all lines. Studies that aimed to identify, for example, targets of the leaf-restricted TF ID1 regulating the transition to flowering support this assumption, as the identified up-and down-regulated genes (Coneva et al, 2007(Coneva et al, , 2012 do not overlap with the genes found in this study. Thus, we conclude that, during adaption to a range of climates, maize lines have evolved distinct severities of the roles of different floral control key players.…”

Florigen-Encoding Genes of Day-Neutral and Photoperiod-Sensitive Maize Are Regulated by Different Chromatin Modifications at the Floral Transition

“…We previously showed that this night break (NB) regimen effectively prevents flowering in teosinte without greatly altering the total amount of light received by nonflowering plants relative to those grown under SD conditions ( Fig. 1; Lazakis et al, 2011;Coneva et al, 2012).…”

“…In this scenario, id1 acts as a gatekeeper that primes floral induction in day-neutral temperate maize. Previous transcriptome comparisons of flowering and nonflowering maize suggest that id1 also regulates genes involved in primary metabolism to establish a physiological state associated with readiness for flowering (Coneva et al, 2007(Coneva et al, , 2012, thus connecting florigen production with metabolic rate to facilitate the transition to reproductive growth.…”

Sugars, the clock and transition to flowering

“…These authors demonstrated that the INDETERMINATE DOMAIN 8 (IDD8) transcription factor plays a role in FT-dependent flowering induction, via modulation of the SuSy4 activity. Further, Coneva et al (2012) reported that the starch to sucrose transition is important during autonomous flowering. In conclusion, sucrose seems to interact in many ways with the flowering network, and further studies are needed to fully understand these connections at the molecular level.…”