KNOTTED1-like Homeobox Transcription Factors Research Articles

Genome-Wide Analysis of KNOX Transcription Factors and Expression Pattern of Dwarf-Related KNOX Genes in Pear.

KNOTTED1-like homeobox (KNOX) transcription factors (TFs) belonging to the homeobox TF family play important roles in plant growth, development, and responses to abiotic and biotic stress. However, little information is available on KNOX TF in pear (Pyrus). In this study, 19 PbKNOXs TFs were re-identified in pear (Pyrus bretschneideri Rehd.). Phylogenetic analysis revealed that the TFs were clustered into three groups with 10 conserved motifs, some of which were group- or subgroup-specific, implying that they are important for the functions of the KNOX in these clades. PbKNM1 and PbKNM2 are KNM (encodes a MEINOX domain but not a homeodomain) genes identified in pear for the first time. KNOX genes in Pyrus and Malus were closely related, and a collinear relationship among PbKNOX genes in Pyrus and Malus was observed. Analysis of the expression patterns of PbKNOX genes in different tissues, at various growth stages, and in response to abiotic and biotic stress revealed that PbKNOXs are involved in plant growth and development. Our comparative transcriptional analysis of dwarf mutant varieties revealed that genes belonging to class I are highly expressed compared with genes in other classes. Analysis of the expression of PbKNOX genes in the hybrid offspring of vigorous and dwarf varieties revealed that PbKNOX genes were highly expressed in the vigorous offspring and weakly expressed in the dwarf offspring. These findings provide new insight into the function of KNOX TFs in pear and will aid future studies of dwarf fruit trees.

Evolutionary Relationships and Divergence of KNOTTED1-Like Family Genes Involved in Salt Tolerance and Development in Cotton (Gossypium hirsutum L.).

The KNOX (KNOTTED1-like homeobox) transcription factors play an important role in leaf, shoot apical meristem and seed development and respond to biotic and abiotic stresses. In this study, we analyzed the diversity and evolutionary history of the KNOX gene family in the genome of tetraploid cotton (Gossypium hirsutum). Forty-four putative KNOX genes were identified. All KNOX genes from seven higher plant species were classified into KNOXI, KNOXII, and KNATM clades based on a phylogenetic analysis. Chromosomal localization and collinearity analysis suggested that whole-genome duplication and a polyploidization event contributed to the expansion of the cotton KNOX gene family. Analyses of expression profiles revealed that the GhKNOX genes likely responded to diverse stresses and were involved in cotton growth developmental processes. Silencing of GhKNOX2 enhanced the salt tolerance of cotton seedlings, whereas silencing of GhKNOX10 and GhKNOX14 reduced seedling tolerance to salt stress. Silencing of GhSTM3 influenced the cotton flowering time and plant development. These findings clarify the evolution of the cotton KNOX gene family and provide a foundation for future functional studies of KNOX proteins in cotton growth and development and response to abiotic stresses.

A salivary effector enables whitefly to feed on host plants by eliciting salicylic acid-signaling pathway

Phloem-feeding insects feed on plant phloem using their stylets. While ingesting phloem sap, these insects secrete saliva to circumvent plant defenses. Previous studies have shown that, to facilitate their feeding, many phloem-feeding insects can elicit the salicylic acid- (SA-) signaling pathway and thus suppress effective jasmonic acid defenses. However, the molecular basis for the regulation of the plant's defense by phloem-feeding insects remains largely unknown. Here, we show that Bt56, a whitefly-secreted low molecular weight salivary protein, is highly expressed in the whitefly primary salivary gland and is delivered into host plants during feeding. Overexpression of the Bt56 gene in planta promotes susceptibility of tobacco to the whitefly and elicits the SA-signaling pathway. In contrast, silencing the whitefly Bt56 gene significantly decreases whitefly performance on host plants and interrupts whitefly phloem feeding with whiteflies losing the ability to activate the SA pathway. Protein-protein interaction assays show that the Bt56 protein directly interacts with a tobacco KNOTTED 1-like homeobox transcription factor that decreases whitefly performance and suppresses whitefly-induced SA accumulation. The Bt56 orthologous genes are highly conserved but differentially expressed in different species of whiteflies. In conclusion, Bt56 is a key salivary effector that promotes whitefly performance by eliciting salicylic acid-signaling pathway.

Evolution, diversification, and expression of KNOX proteins in plants.

The KNOX (KNOTTED1-like homeobox) transcription factors play a pivotal role in leaf and meristem development. The majority of these proteins are characterized by the KNOX1, KNOX2, ELK, and homeobox domains whereas the proteins of the KNATM family contain only the KNOX domains. We carried out an extensive inventory of these proteins and here report on a total of 394 KNOX proteins from 48 species. The land plant proteins fall into two classes (I and II) as previously shown where the class I family seems to be most closely related to the green algae homologs. The KNATM proteins are restricted to Eudicots and some species have multiple paralogs of this protein. Certain plants are characterized by a significant increase in the number of KNOX paralogs; one example is Glycine max. Through the analysis of public gene expression data we show that the class II proteins of this plant have a relatively broad expression specificity as compared to class I proteins, consistent with previous studies of other plants. In G. max, class I protein are mainly distributed in axis tissues and KNATM paralogs are overall poorly expressed; highest expression is in the early plumular axis. Overall, analysis of gene expression in G. max demonstrates clearly that the expansion in gene number is associated with functional diversification.

Plant hormones and homeoboxes: bridging the gap?

Plant hormones are signalling molecules that control growth and development. Growth of the aerial parts of higher plants requires the continuous activity of the shoot apical meristem, a small mound of cells at the apex of a plant. KNOTTED1-like HOMEOBOX (KNOX) genes are involved in regulating meristem activity, however, little is known about how this regulation is mediated. Recent evidence suggests that KNOX transcription factors may control meristem development by regulating the balance of activities of multiple hormones.

The Gibberellin Pathway Mediates KNOTTED1-Type Homeobox Function in Plants with Different Body Plans

Background: The shoot apical meristem (SAM) is an indeterminate structure that gives rise to the aerial parts of higher plants. Leaves arise from the differentiation of cells at the flanks of the SAM. Current evidence suggests that the precise regulation of KNOTTED1-like homeobox (KNOX) transcription factors is central to the acquisition of leaf versus meristem identity in a wide spectrum of plant species. Factors required to repress KNOX gene expression in leaves have recently been identified. Additional factors such as the CHD3 chromatin remodeling factor PICKLE (PKL) act to restrict meristematic activity in Arabidopsis leaves without repressing KNOX gene expression. Less is known regarding downstream targets of KNOX function. Recent evidence, however, has suggested that growth regulators may mediate KNOX activity in a variety of plant species.Results: Here we show that reduced activity of the gibberellin (GA) growth regulator pathway promotes meristematic activity, both in the natural context of KNOX function in the SAM and upon ectopic KNOX expression in Arabidopsis leaves. We show that constitutive signaling through the GA pathway is detrimental to meristem maintenance. Furthermore, we provide evidence that one of the functions of the KNOX protein SHOOTMERISTEMLESS (STM) is to exclude transcription of the GA-biosynthesis gene AtGA20ox1 from the SAM. We also demonstrate that AtGA20ox1 transcript is reduced in the pkl mutant in a KNOX-independent manner. Moreover, we show a similar interaction between KNOX proteins and GA-biosynthesis gene expression in the tomato leaf and implicate this interaction in regulation of the dissected leaf form.Conclusions: We suggest that repression of GA activity by KNOX transcription factors is a key component of meristem function. Transfer of the KNOX/GA regulatory module from the meristem to the leaf may have contributed to the generation of the diverse leaf morphologies observed in higher plants.