Rice florigens control a common set of genes at the shoot apical meristem including the F-BOX BROADER TILLER ANGLE 1 that regulates tiller angle and spikelet development.

Rice flowering is triggered by transcriptional reprogramming at the shoot apical meristem (SAM) mediated by florigenic proteins produced in leaves in response to changes in photoperiod. Florigens are more rapidly expressed under short days (SDs) compared to long days (LDs) and include the HEADING DATE 3a (Hd3a) and RICE FLOWERING LOCUS T1 (RFT1) phosphatidylethanolamine binding proteins. Hd3a and RFT1 are largely redundant at converting the SAM into an inflorescence, but whether they activate the same target genes and convey all photoperiodic information that modifies gene expression at the SAM is currently unclear. We uncoupled the contribution of Hd3a and RFT1 to transcriptome reprogramming at the SAM by RNA sequencing of dexamethasone-inducible over-expressors of single florigens and wild-type plants exposed to photoperiodic induction. Fifteen highly differentially expressed genes common to Hd3a, RFT1, and SDs were retrieved, 10 of which still uncharacterized. Detailed functional studies on some candidates revealed a role for LOC_Os04g13150 in determining tiller angle and spikelet development and the gene was renamed BROADER TILLER ANGLE 1 (BRT1). We identified a core set of genes controlled by florigen-mediated photoperiodic induction and defined the function of a novel florigen target controlling tiller angle and spikelet development.

Environmental control of rice flowering time.

Correct measurement of environmental parameters is fundamental for plant fitness and survival, as well as for timing developmental transitions, including the switch from vegetative to reproductive growth. Important parameters that affect flowering time include day length (photoperiod) and temperature. Their response pathways have been best described in Arabidopsis, which currently offers a detailed conceptual framework and serves as a comparison for other species. Rice, the focus of this review, also possesses a photoperiodic flowering pathway, but 150 million years of divergent evolution in very different environments have diversified its molecular architecture. The ambient temperature perception pathway is strongly intertwined with the photoperiod pathway and essentially converges on the same genes to modify flowering time. When observing network topologies, it is evident that the rice flowering network is centered on EARLY HEADING DATE 1, a rice-specific transcriptional regulator. Here, we summarize the most important features of the rice photoperiodic flowering network, with an emphasis on its uniqueness, and discuss its connections with hormonal, temperature perception, and stress pathways.

Heterologous microProtein expression identifies LITTLE NINJA, a dominant regulator of jasmonic acid signaling.

MicroProteins are small, often single-domain proteins that are sequence-related to larger, often multidomain proteins. Here, we used a combination of comparative genomics and heterologous synthetic misexpression to isolate functional cereal microProtein regulators. Our approach identified LITTLE NINJA (LNJ), a microProtein that acts as a modulator of jasmonic acid (JA) signaling. Ectopic expression of LNJ in Arabidopsis resulted in stunted plants that resembled the decuple JAZ (jazD) mutant. In fact, comparing the transcriptomes of transgenic LNJ overexpressor plants and jazD revealed a large overlap of deregulated genes, suggesting that ectopic LNJ expression altered JA signaling. Transgenic Brachypodium plants with elevated LNJ expression levels showed deregulation of JA signaling as well and displayed reduced growth and enhanced production of side shoots (tiller). This tillering effect was transferable between grass species, and overexpression of LNJ in barley and rice caused similar traits. We used a clustered regularly interspaced short palindromic repeats (CRISPR) approach and created a LNJ-like protein in Arabidopsis by deleting parts of the coding sentence of the AFP2 gene that encodes a NINJA-domain protein. These afp2-crispr mutants were also stunted in size and resembled jazD Thus, similar genome-engineering approaches can be exploited as a future tool to create LNJ proteins and produce cereals with altered architectures.

Light affects tissue patterning of the hypocotyl in the shade-avoidance response.

Plants have evolved strategies to avoid shade and optimize the capture of sunlight. While some species are tolerant to shade, plants such as Arabidopsis thaliana are shade-intolerant and induce elongation of their hypocotyl to outcompete neighboring plants. We report the identification of a developmental module acting downstream of shade perception controlling vascular patterning. We show that Arabidopsis plants react to shade by increasing the number and types of water-conducting tracheary elements in the vascular cylinder to maintain vascular density constant. Mutations in genes affecting vascular patterning impair the production of additional xylem and also show defects in the shade-induced hypocotyl elongation response. Comparative analysis of the shade-induced transcriptomes revealed differences between wild type and vascular patterning mutants and it appears that the latter mutants fail to induce sets of genes encoding biosynthetic and cell wall modifying enzymes. Our results thus set the stage for a deeper understanding of how growth and patterning are coordinated in a dynamic environment.