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Alternative splicing (AS) generates multiple transcripts from the same gene, however, AS contribution to proteome complexity remains elusive in plants. AS is prevalent under stress conditions in plants, but it is counterintuitive why plants would invest in protein synthesis under declining energy supply. We propose that plants employ AS not only to potentially increasing proteomic complexity, but also to buffer against the stress-responsive transcriptome to reduce the metabolic cost of translating all AS transcripts. To maximise efficiency under stress, plants may make fewer proteins with disordered domains via AS to diversify substrate specificity and maintain sufficient regulatory capacity. Furthermore, we suggest that chromatin state-dependent AS engenders short/long-term stress memory to mediate reproducible transcriptional response in the future. Crown Copyright © 2019. Published by Elsevier Ltd. All rights reserved.

RNA-protein interaction is an important checkpoint to tune gene expression at the RNA level. Global identification of proteins binding in vivo to mRNA has been possible through interactome capture - where proteins are fixed to target RNAs by UV crosslinking and purified through affinity capture of polyadenylated RNA. In Arabidopsis over 500 RNA-binding proteins (RBPs) enriched in UV-crosslinked samples have been identified. As in mammals and yeast, the mRNA interactomes came with a few surprises. For example, a plethora of the proteins caught on RNA had not previously been linked to RNA-mediated processes, for example proteins of intermediary metabolism. Thus, the studies provide unprecedented insights into the composition of the mRNA interactome, highlighting the complexity of RNA-mediated processes.

The decision about when to flower is a crucial one for plants that depend on meeting optimal environmental conditions for pollination and seed maturation. Many plants use daylength – the photoperiod – as the main indicator of seasonal progression. In the 1930s, Erwin Bunning proposed that plants rely on their endogenous timekeeper – the circadian clock – to monitor the duration of day and night. The clock would set an endogenous rhythm in light responsiveness and, depending upon in which of its phases plants see daylight, flower induction would be triggered or not. Thus, this clock is also a clock for all seasons. Experimental support came from the discovery of mutants in the long-day plant Arabidopsis that were disrupted in circadian rhythmicity and in timing of flowering.George Coupland's team 1xCONSTANS mediates between the circadian clock and the control of flowering in Arabidopsis. Suarez-Lopez, P. et al. Nature. 2001; 410: 1116–1120Crossref | PubMed | Scopus (686)See all References1 now takes this a step further, bridging a gap between the endogenous clock and the photoperiodic response: the zinc-finger transcription factor, CONSTANS (CO), promotes flowering specifically in long-days. Suarez-Lopez et al. 1xCONSTANS mediates between the circadian clock and the control of flowering in Arabidopsis. Suarez-Lopez, P. et al. Nature. 2001; 410: 1116–1120Crossref | PubMed | Scopus (686)See all References1 show that the abundance of CO mRNA undergoes circadian oscillations. The wave form depends on the daylength: under short-days, the CO peak is largely confined to darkness, whereas under inductive long-days, levels of CO are high during most of the light period. In the late-flowering gi-3 (gigantea) mutant, CO oscillates with a lower amplitude, and in the lhy (late elongated hypocotyl) mutant, CO is expressed at a reduced level with a different phase. The late-flowering phenotypes are corrected by overexpressing CO in the mutant backgrounds. Conversely, CO oscillates at a higher level in the early-flowering elf3 mutant. Because LHY, GI and ELF3 are all part of the endogenous clock system, the clock presumably exerts its control of the photoperiodic response by setting the CO rhythm. CO, in turn, promotes flowering via downstream genes. Indeed, it causes an immediate target, FT, to oscillate with a similar phase. The FT peak is lacking in gi-3 and lhy mutants but elevated in elf3. It seems likely that, at its peak phase, CO activates FT, presumably through its zinc-finger DNA-binding domain.CO might be the missing link to understand of how daylength interpreted through the clock influences flowering: following Bunning's concept, photoperiod-dependent CO phasing is consistent with the view that the CO rhythm is the molecular basis for differential light sensitivity. High CO levels coincide with light in long-days but are largely confined to darkness in short-days. It is seductive to implicate CO also as a direct target of light regulation. Light impinging on CO at the post-transcriptional level might influence its abundance or activity, accelerating flowering under long-days. Thus, light's dual role in setting the rhythm in photoinducibility through the clock, as well as activating flowering in the promotive phase, could be mediated by CO. A further issue will be how CO as a key player of the photoperiodic route would integrate with the alternative pathways promoting flowering independent of daylength in Arabidopsis.