Regulation of flowering time in Brachypodium distachyon

GONZALO, L; MACHADO, R; EUSEBI, D; GÜNTHARDT, MM; MUCHUT, SE; REUTEMANN, AG; VEGETTI, AC; VOGEL, JP; UBERTI-MANASSERO, NG

Huesca

Congreso; 4th International Brachypodium Conference; 2019

In higher plants, phase transition from vegetative to reproductive development is tightlycoordinated through networks that integrate internal and external stimuli. PANICLEPHYTOMER2 (PAP2) is a SEPALLATA-like protein that plays an important role inregulating rice meristems and floral organ identity (Kobayashi et al., 2012). It promotes thephase changes of the shoot apical meristem from vegetative to inflorescence meristem,acting together with AP1-like proteins to negatively regulate RCN4 (TFL1 orthologue) in aconserved pathway between Arabidopsis thaliana and rice (Liu et al., 2013). In this work,we study the role of the Brachypodium distachyon gene BdPAP2 in regulating floweringtime. In order to achieve this goal, we first over-expressed BdPAP2 in A. thaliana plants.Transgenic plants showed an earlier transition from vegetative to reproductive state and,consequently, developed fewer rosette leaves than control plants. This phenotype wascorrelated with increased expression levels of the floral integrators SOC1 and FT.Interestingly, TFL1 expression levels were significantly reduced in these plants, suggestinga possible functional conservation in the pathway reported for A. thaliana and rice. Wealso analyzed two independent BdPAP2 mutant lines of B. distachyon. One of the linescarries a T-DNA insertion that introduced a 4xCaMV35S enhancer sequence in an intronof BdPAP2, upregulating its expression. This activation tagged line flowered earlier anddeveloped fewer leaves than control plants. The other mutant was a sodium azide mutantthat contains a SNP mutation in a splice-site donor that is expected to disrupt BdPAP2function. As expected, this mutant showed a delay in flowering time. Our results obtainedin A. thaliana and B. distachyon suggest that BdPAP2 controls flowering time by regulatingthe B. distachyon TFL1 orthologue, BdRCN4. As a first attempt to test this hypothesis, westudied the 3` distal region of TFL1 homologues of B. distachyon. We found the putativeregulatory boxes in all the three genes analyzed, in a similar number and disposition ofthose found in A. thaliana. We are now focusing our efforts in corroborating if BdRCN4 is adirect target of BdPAP2, as well as if this regulation depends on the interaction of BdPAP2and AP1-like proteins. This research will shed new light on the pathways that regulateflowering time in grasses.