miR319a targeting of TCP4 is critical for petal growth and development in Arabidopsis

Abstract

In a genetic screen in a drnl-2 background, we isolated a loss-offunction allele in miR319a (miR319a 129 ). Previously, miR319a has been postulated to play a role in leaf development based on the dramatic curled-leaf phenotype of plants that ectopically express miR319a (jaw-D). miR319a 129 mutants exhibit defects in petal and stamen development; petals are narrow and short, and stamens exhibit defects in anther development. The miR319a 129 loss-of-function allele contains a single-base change in the middle of the encoded miRNA, which reduces the ability of miR319a to recognize targets. Analysis of the expression patterns of the three members of the miR319 gene family (miR319a, miR319b, and miR319c) indicates that these genes have largely non-overlapping expression patterns suggesting that these genes have distinct developmental functions. miR319a functions by regulating the TCP transcription factors TCP2, TCP3, TCP4, TCP10, and TCP24; the level of RNA expression of these TCP genes is down-regulated in jaw-D and elevated in miR319a 129 . Several lines of evidence demonstrate that TCP4 is a key target of miR319a. First, the tcp4 soj6 mutant, which contains a mutation in the TCP4 miRNAbinding site complementary to the miR319a 129 mutation, suppresses the flower phenotype of miR319a 129 . Second, expression of wild-type TCP4 in petals and stamens (i.e., AP3:TCP4) has no effect on flower development; by contrast, a miRNA-resistant version of TCP4, when expressed in petals and stamens (i.e., pAP3:mTCP4) causes these organs not to develop. Surprisingly, when AP3:TCP4 is present in a miR319a 129 background, petal and stamen development is severely disrupted, suggesting that proper regulation by miR319a of TCP4 is critical in these floral organs.DRNL ͉ flower development ͉ forward genetics ͉ microRNA ͉ stamen M icroRNAs (miRNAs) are 21-24 nucleotide regulatory RNAs that function in diverse aspects of plant biology (1) such as biotic and abiotic stress responses (2), metabolism (3), hormone signaling (4), transcription (5), development (6), and the regulation of miRNA machinery itself (7,8). Most studies of plant miRNAs focus on alleles that ectopically express the miRNA. In miRNA overexpression lines, the RNA levels of target genes are downregulated resulting in a phenotype that mimics the loss-of-function phenotypes of miRNA target mutants (9, 10). Loss-of-function alleles in miRNA genes are rare because most often miRNAs are redundantly encoded in plant genomes. Thus, mutation of a single miRNA gene usually does not result in a mutant phenotype. In the few miRNA loss-of-function mutants that are available (5,6,11,12), the RNA levels of target genes are elevated, which is expected if the miRNA can no longer function to degrade target mRNAs. miR319a was initially characterized based on the dramatic leaf phenotype that results from overexpression of miR319a, as in the jaw-D allele that results in a jagged and wavy (jaw) leaf-phenotype (13). The best-characterized targets of miR319 are a subset of TCP transcription factors...

The Cotton Transcription Factor TCP14 Functions in Auxin-Mediated Epidermal Cell Differentiation and Elongation

“…In particular, great progress has been made in functional characterization of the class II TCPs in Arabidopsis. These transcription factors play important roles in leaf, flower, shoot morphogenesis, and hormone biosynthesis (Damerval et al, 2007;Koyama et al, 2007;Schommer et al, 2008;Nag et al, 2009;Guo et al, 2010). The cellular functions of class I TCPs are less well explored, but several previous studies indicated that they are involved in a number of cellular or developmental processes.…”

Impact of InMIR319 and light on the expression of InTCP4 gene involved in the development of Ipomoea nil plants

“…In apexes, there are transcripts of both genes, which is probably associated with their participation in the regulation forming the leaves, as described in tomato (Ori et al 2007). In A. thaliana, there are three genes encoding miR319 (MIR319a, -b, -c), MIR319a and MIR319b encoding identical mature miRNA and the expression patterns for the three MIR319 genes are distinct, suggesting that these genes may have largely unique developmental functions (Nag et al 2009;Schommer et al 2012). It can therefore be assumed that other unidentified MIR319 genes also exist in I. nil that may influence the accumulation of mRNA InTCP4 in other tissues.…”

“…2a) and InMIR319 indicates a similar tissue expression pattern to MIR319a and MIR319b in A. thaliana (Nag et al 2009). The results of Nag et al (2009) suggest that miR319a/b might not play an important role in leaf development, but in petal and stamen development. In A. thaliana jaw-D mutants (overexpression of MIR319 gene) have slightly shorter hypocotyls than wildtype plants, whereas increased TCP activity leads to longer hypocotyls (Palatnik et al 2003;Schommer et al 2008;Sarvepalli and Nath 2011).…”

“…Identified In-pre-miR319 contains a sequence of mature miRNA319 identical to miR319a/b A. thaliana (Fig. 2a) and InMIR319 indicates a similar tissue expression pattern to MIR319a and MIR319b in A. thaliana (Nag et al 2009). The results of Nag et al (2009) suggest that miR319a/b might not play an important role in leaf development, but in petal and stamen development.…”

“…The high level of InTCP4 transcript in pistils seems to be a particularly interesting fact because of the lack of reports of involvement of homologues of TCP4 in the development of this organ. TCP4 and miR319a, A. thaliana regulate the normal development of stamens and petals (Schommer et al 2008;Nag et al 2009). Analysis of cin mutants in Antirrhinum showed that the miRNA-regulated TCP gene, CIN, affects petal lobe development by controlling epidermal cell differentiation and growth (Crawford et al 2004).…”