PHOSPHORYLETHANOLAMINE CYTIDYLYLTRANSFERASE 1 modulates flowering in a florigen-independent manner by regulating SVP.

PHOSPHORYLETHANOLAMINE CYTIDYLYLTRANSFERASE 1 (PECT1) regulates phosphatidylethanolamine biosynthesis and controls the phosphatidylethanolamine:phosphatidylcholine ratio in Arabidopsis thaliana Previous studies have suggested that PECT1 regulates flowering time by modulating the interaction between phosphatidylcholine and FLOWERING LOCUS T (FT), a florigen, in the shoot apical meristem (SAM). Here, we show that knockdown of PECT1 by artificial microRNA in the SAM (pFD::amiR-PECT1) accelerated flowering under inductive and even non-inductive conditions, in which FT transcription is almost absent, and in ft-10 twin sister of ft-1 double mutants under both conditions. Transcriptome analyses suggested that PECT1 affects flowering by regulating SHORT VEGETATIVE PHASE (SVP) and GIBBERELLIN 20 OXIDASE 2 (GA20ox2). SVP misexpression in the SAM suppressed the early flowering of pFD::amiR-PECT1 plants. pFD::amiR-PECT1 plants showed increased gibberellin (GA) levels in the SAM, concomitant with the reduction of REPRESSOR OF GA1-3 levels. Consistent with this, GA treatment had little effect on flowering time of pFD::amiR-PECT1 plants and the GA antagonist paclobutrazol strongly affected flowering in these plants. Together, these results suggest that PECT1 also regulates flowering time through a florigen-independent pathway, modulating SVP expression and thus regulating GA production.

Generation and Transcriptome Profiling of Slr1-d7 and Slr1-d8 Mutant Lines with a New Semi-Dominant Dwarf Allele of SLR1 Using the CRISPR/Cas9 System in Rice.

The rice SLR1 gene encodes the DELLA protein, and a loss-of-function mutation is dwarfed by inhibiting plant growth. We generate slr1-d mutants with a semi-dominant dwarf phenotype to target mutations of the DELLA/TVHYNP domain using CRISPR/Cas9 genome editing in rice. Sixteen genetic edited lines out of 31 transgenic plants were generated. Deep sequencing results showed that the mutants had six different mutation types at the target site of the TVHYNP domain of the SLR1 gene. The homo-edited plants selected individuals without DNA (T-DNA) transcribed by segregation in the T1 generation. The slr1-d7 and slr1-d8 plants caused a gibberellin (GA)-insensitive dwarf phenotype with shrunken leaves and shortened internodes. A genome-wide gene expression analysis by RNA-seq indicated that the expression levels of two GA-related genes, GA20OX2 (Gibberellin oxidase) and GA3OX2, were increased in the edited mutant plants, suggesting that GA20OX2 acts as a convert of GA12 signaling. These mutant plants are required by altering GA responses, at least partially by a defect in the phytohormone signaling system process and prevented cell elongation. The new mutants, namely, the slr1-d7 and slr1-d8 lines, are valuable semi-dominant dwarf alleles with potential application value for molecule breeding using the CRISPR/Cas9 system in rice.

The rice YABBY4 gene regulates plant growth and development through modulating the gibberellin pathway.

YABBY genes encode seed plant-specific transcription factors that play pivotal roles in diverse aspects of leaf, shoot, and flower development. Members of the YABBY gene family are primarily expressed in lateral organs in a polar manner and function to specify abaxial cell fate in dicotyledons, but this polar expression is not conserved in monocotyledons. The function of YABBY genes is therefore not well understood in monocotyledons. Here we show that overexpression of the rice (Oryza sativa L.) YABBY4 gene (OsYABBY4) leads to a semi-dwarf phenotype, abnormal development in the uppermost internode, an increased number of floral organs, and insensitivity to gibberellin (GA) treatment. We report on an important role for OsYABBY4 in negative control of the expression of a GA biosynthetic gene by binding to the promoter region of the gibberellin 20-oxidase 2 gene (GA20ox2), which is a direct target of SLR1 (the sole DELLA protein negatively controlling GA responses in rice). OsYABBY4 also suppresses the expression level of SLR1 and interacts with SLR1 protein. The interaction inhibits GA-dependent degradation of SLR1 and therefore leads to GA insensitivity. These data together suggest that OsYABBY4 serves as a DNA-binding intermediate protein for SLR1 and is associated with the GA signaling pathway regulating gene expression during plant growth and development.

Identification of GA20ox2 as a target of ATHB2 and TCP13 during shade response.

The shade avoidance syndrome (SAS) is a collective adaptive response of plants under shade highlighted by characteristic phenotypes such as hypocotyl elongation, which is largely mediated by concerted actions of auxin and GA. We identified ATHB2, a homeodomain-leucine zipper (HD-Zip) domain transcription factor known to be rapidly induced under shade condition, as a positive regulator of GA biosynthesis necessary for the SAS by transactivating the expression of GA20ox2, a key gene in the GA biosynthesis pathway. Based on promoter deletion analysis, EMSA and ChIP assay, ATHB2 appears to regulate the GA20ox2 expression as a direct binding target. We also found that the GA20ox2 expression is under negative control by TCP13, the effect of which can be suppressed by presence of ATHB2. Considering a rapid induction kinetics of ATHB2, this relationship between ATHB2 and TCP13 may allow ATHB2 to play a shade-specific activator for GA20ox by derepressing a pre-existing activity of TCP13.