The Class II KNOX family members KNAT3 and KNAT7 redundantly participate in Arabidopsis seed coat mucilage biosynthesis

AGAMOUS-LIKE24 controls pistil number in Japanese apricot by targeting the KNOTTED1-LIKE gene KNAT2/6-a

The formation of multi-pistil flowers reduces the yield and quality in Japanese apricot (Prunus mume). However, the molecular mechanism underlying the formation of multi-pistil flowers remains unknown. In the current study, overexpression of PmKNAT2/6-a, a class I KNOTTED1-like homeobox (KNOX) member, in Arabidopsis (Arabidopsis thaliana) resulted in a multi-pistil phenotype. Analysis of the upstream regulators of PmKNAT2/6-a showed that AGAMOUS-like 24 (PmAGL24) could directly bind to the PmKNAT2/6-a promoter and regulate its expression. PmAGL24 also interacted with Like Heterochromatin Protein 1 (PmLHP1) to recruit lysine trimethylation at position 27 on histone H3 (H3K27me3) to regulate PmKNAT2/6-a expression, which is indirectly involved in multiple pistils formation in Japanese apricot flowers. Our study reveals that the PmAGL24 transcription factor, an upstream regulator of PmKNAT2/6-a, regulates PmKNAT2/6-a expression via direct and indirect pathways and is involved in the formation of multiple pistils in Japanese apricot.

KNOTTED1-like homeobox (KNOX) transcription factors - Hubs in a plethora of networks: A review

KNOX (KNOTTED1-like HOMEOBOX) belongs to a class of important homeobox genes, which encode the homeodomain proteins binding to the specific element of target genes, and widely participate in plant development. Advancements in genetics and molecular biology research generate a large amount of information about KNOX genes in model and non-model plants, and their functions in different developmental backgrounds are gradually becoming clear. In this review, we summarize the known and presumed functions of the KNOX gene in plants, focusing on horticultural plants and crops. The classification and structural characteristics, expression characteristics and regulation, interacting protein factors, functions, and mechanisms of KNOX genes are systematically described. Further, the current research gaps and perspectives were discussed. These comprehensive data can provide a reference for the directional improvement of agronomic traits through KNOX gene regulation.

Identification and expression analysis of the KNOX genes during organogenesis and stress responseness in Camellia sinensis (L.) O. Kuntze

Tea plant (Camellia sinensis L.), whose leaves are the major reproductive organs, has been cultivated and consumed widely for its economic and health benefits. The Knotted1-like Homeobox (KNOX) proteins play significant roles in leaf morphology formation and development. However, the functions of KNOX proteins in tea plants are still unknown. Here, 11 CsKNOX genes from the tea plants were cloned and divided into Class I, II, and KNATM clades based on their protein sequences. These 11 CsKNOX genes were mapped on 8 out of 15 tea plant chromosomes, all localized in the nucleus. Specific spatiotemporal expression patterns of CsKNOX genes were found in various tissues and different development periods of buds, flowers, and roots of tea plants. Meanwhile, transcript levels of CsKNOX in tea leaves were strongly correlated with the accumulation of flavan-3-ols and proanthocyanidins. It was found that most of the CsKNOX genes could respond to drought, salt, cold, and exogenous MeJA and GA3 by analysis of transcriptomics data and promoter elements. The protein interaction analysis showed that CsKNOX could cooperate with CsAS1 and other critical functional proteins. In conclusion, this research provided the basic information for the functions of the CsKNOX family during organogenesis and stress response in tea plants, which was necessary for further functional characterization verification.

AtHSPR functions in gibberellin-mediated primary root growth by interacting with KNAT5 and OFP1 in Arabidopsis

KEY MESSAGE

AtHSPR forms a complex with KNAT5 and OFP1 to regulate primary root growth through GA-mediated root meristem activity. KNAT5-OFP1 functions as a negative regulator of AtHSPR in response to GA. Plant root growth is modulated by gibberellic acid (GA) signaling and depends on root meristem maintenance. ARABIDOPSIS THALIANA HEAT SHOCK PROTEIN-RELATED (AtHSPR) is a vital regulator of flowering time and salt stress tolerance. However, little is known about the role of AtHSPR in the regulation of primary root growth. Here, we report that athspr mutant exhibits a shorter primary root compared to wild type and that AtHSPR interacts with KNOTTED1-LIKE HOMEOBOX GENE 5 (KNAT5) and OVATE FAMILY PROTEIN 1 (OFP1). Genetic analysis showed that overexpression of KNAT5 or OFP1 caused a defect in primary root growth similar to that of the athspr mutant, but knockout of KNAT5 or OFP1 rescued the short root phenotype in the athspr mutant by altering root meristem activity. Further investigation revealed that KNAT5 interacts with OFP1 and that AtHSPR weakens the inhibition of GIBBERELLIN 20-OXIDASE 1 (GA20ox1) expression by the KNAT5-OFP1 complex. Moreover, root meristem cell proliferation and root elongation in 35S::KNAT5athspr and 35S::OFP1athspr seedlings were hypersensitive to GA3 treatment compared to the athspr mutant. Together, our results demonstrate that the AtHSPR-KNAT5-OFP1 module regulates root growth and development by impacting the expression of GA biosynthetic gene GA20ox1, which could be a way for plants to achieve plasticity in response to the environment.

The role of Class Ⅱ KNOX family in controlling compound leaf patterning in Medicago truncatula

Compound leaf development requires the coordination of genetic factors, hormones, and other signals. In this study, we explored the functions of Class Ⅱ KNOTTED-like homeobox (KNOXII) genes in the model leguminous plant Medicago truncatula. Phenotypic and genetic analyses suggest that MtKNOX4, 5 are able to repress leaflet formation, while MtKNOX3, 9, 10 are not involved in this developmental process. Further investigations have shown that MtKNOX4 represses the CK signal transduction, which is downstream of MtKNOXⅠ-mediated CK biosynthesis. Additionally, two boundary genes, FUSED COMPOUND LEAF1 (orthologue of Arabidopsis Class M KNOX) and NO APICAL MERISTEM (orthologue of Arabidopsis CUP-SHAPED COTYLEDON), are necessary for MtKNOX4-mediated compound leaf formation. These findings suggest, that among the members of MtKNOXⅡ, MtKNOX4 plays a crucial role in integrating the CK pathway and boundary regulators, providing new insights into the roles of MtKNOXⅡ in regulating the elaboration of compound leaves in M. truncatula.

Expression dynamics and a loss-of-function of Arabidopsis RabC1 GTPase unveil its role in plant growth and seed development

Transcript isoform dynamics, spatiotemporal expression, and mutational analysis uncover that Arabidopsis RabC1 GTPase is required for root length, flowering time, seed size, and seed mucilage. Rab GTPases are crucial regulators for moving different molecules to their specific compartments according to the needs of the cell. In this work, we illustrate the role of RabC1 GTPase in Arabidopsis growth and seed development. We identify and analyze the expression pattern of three transcript isoforms of RabC1 in different development stages, along with their tissue-specific transcript abundance. The promoter activity of RabC1 using promoter-GUS fusion shows that it is widely expressed during the growth of Arabidopsis, particularly in seed tissues such as chalazal seed coat and chalazal endosperm. Lack of RabC1 function led to shorter roots, lesser biomass, delayed flowering, and sluggish plant development. The mutants had smaller seeds than the wildtype, less seed mass, and lower seed coat permeability. Developing seeds also revealed a smaller endosperm cavity and shorter integument cells. Additionally, we found that the knock-out mutant had downregulated expression of genes implicated in the transit of sugars and amino acids from maternal tissue to developing seed. The seeds of the loss-of-function mutant had reduced seed mucilage. All the observed mutant phenotypes were restored in the complemented lines confirming the function of RabC1 in seed development and plant growth.

Transcription factors KNAT3 and KNAT4 are essential for integument and ovule formation in Arabidopsis

Integuments form important protective cell layers surrounding the developing ovules in gymno- and angiosperms. Although several genes have been shown to influence the development of integuments, the transcriptional regulatory mechanism is still poorly understood. In this work, we report that the Class II KNOTTED1-LIKE HOMEOBOX (KNOX II) transcription factors KNOTTED1-LIKE HOMEBOX GENE 3 (KNAT3) and KNAT4 regulate integument development in Arabidopsis (Arabidopsis thaliana). KNAT3 and KNAT4 were co-expressed in inflorescences and especially in young developing ovules. The loss-of-function double mutant knat3 knat4 showed an infertility phenotype, in which both inner and outer integuments of the ovule are arrested at an early stage and form an amorphous structure as in the bell1 (bel1) mutant. The expression of chimeric KNAT3- and KNAT4-EAR motif repression domain (SRDX repressors) resulted in severe seed abortion. Protein-protein interaction assays demonstrated that KNAT3 and KNAT4 interact with each other and also with INNER NO OUTER (INO), a key transcription factor required for the outer integument formation. Transcriptome analysis showed that the expression of genes related with integument development is influenced in the knat3 knat4 mutant. The knat3 knat4 mutant also had a lower indole-3-acetic acid (IAA) content, and some auxin signaling pathway genes were downregulated. Moreover, transactivation analysis indicated that KNAT3/4 and INO activate the auxin signaling gene IAA INDUCIBLE 14 (IAA14). Taken together, our study identified KNAT3 and KNAT4 as key factors in integument development in Arabidopsis.

The Identification and Characterization of the KNOX Gene Family as an Active Regulator of Leaf Development in Trifolium repens

Leaves are the primary and critical feed for herbivores. They directly determine the yield and quality of legume forage. Trifolium repens (T. repens) is an indispensable legume species, widely cultivated in temperate pastures due to its nutritional value and nitrogen fixation. Although the leaves of T. repens are typical trifoliate, they have unusual patterns to adapt to herbivore feeding. The number of leaflets in T. repens affects its production and utilization. The KNOX gene family encodes transcriptional regulators that are vital in regulating and developing leaves. Identification and characterization of TrKNOX gene family as an active regulator of leaf development in T. repens were studied. A total of 21 TrKNOX genes were identified from the T. repens genome database and classified into three subgroups (Class I, Class II, and Class M) based on phylogenetic analysis. Nineteen of the genes identified had four conserved domains, except for KNOX5 and KNOX9, which belong to Class M. Varying expression levels of TrKNOX genes were observed at different developmental stages and complexities of leaves. KNOX9 was observed to upregulate the leaf complexity of T. repens. Research on TrKNOX genes could be novel and further assist in exploring their functions and cultivating high-quality T. repens varieties.

Rhamnogalacturonan-I forms mucilage: behind its simplicity, a cutting-edge organization

Zhang Y, Yin Q, Qin W, Gao H, Du J, Chen J, Li H, Zhou G, Wu H, Wu A-M. 2022. The Class II KNOX family members KNAT3 and KNAT7 redundantly participate in Arabidopsis seed coat mucilage biosynthesis. Journal of Experimental Botany 73, 3477–3495.