Understanding the Modus Operandi of Class II KNOX Transcription Factors in Secondary Cell Wall Biosynthesis

Abstract

Lignocellulosic biomass from the secondary cell walls of plants has a veritable potential to provide some of the most appropriate raw materials for producing second-generation biofuels. Therefore, we must first understand how plants synthesize these complex secondary cell walls that consist of cellulose, hemicellulose, and lignin in order to deconstruct them later on into simple sugars to produce bioethanol via fermentation. Knotted-like homeobox (KNOX) genes encode homeodomain-containing transcription factors (TFs) that modulate various important developmental processes in plants. While Class I KNOX TF genes are mainly expressed in the shoot apical meristems of both monocot and eudicot plants and are involved in meristem maintenance and/or formation, Class II KNOXTF genes exhibit diverse expression patterns and their precise functions have mostly remained unknown, until recently. The expression patterns of Class II KNOX TF genes in Arabidopsis, namely KNAT3, KNAT4, KNAT5, and KNAT7, suggest that TFs encoded by at least some of these genes, such as KNAT7 and KNAT3, may play a significant role in secondary cell wall formation. Specifically, the expression of the KNAT7 gene is regulated by upstream TFs, such as SND1 and MYB46, while KNAT7 interacts with other cell wall proteins, such as KNAT3, MYB75, OFPs, and BLHs, to regulate secondary cell wall formation. Moreover, KNAT7 directly regulates the expression of some xylan synthesis genes. In this review, we summarize the current mechanistic understanding of the roles of Class II KNOX TFs in secondary cell wall formation. Recent success with the genetic manipulation of Class II KNOX TFs suggests that this may be one of the biotechnological strategies to improve plant feedstocks for bioethanol production.

Single-cell transcriptome analysis dissects lncRNA-associated gene networks in Arabidopsis

“…We were therefore able to infer the potential roles of lncRNAs in cell-specific functions on the basis of their co-expression patterns with PCs when lncRNAs and PCs were regulated by a common set of upstream regulators. In xylem cells, our analysis identified the regulons of ANAC007 ( VND7 ) and ANAC030 ( VND4 ) ( Figure 5 A and 5B)—NAC-domain TFs necessary for xylem formation ( Kubo et al., 2005 )—and xylem-specific regulons of MYB103 , MYB46 , and ANAC073 ( SND2 )—TFs that regulate secondary wall biosynthesis in xylem tissues ( Ohman et al., 2013 ; Zhong et al., 2021 ; Nookaraju et al., 2022 ). The predicted target (protein-coding) genes of these regulons, including WOX14 ( Denis et al, 2017 ) and ANAC075 ( SND4 ) ( Zhong et al., 2021 ), were functionally enriched in biological pathways related to “xylem development” ( Figure 5 C).…”

<i>In Silico</i> Analysis of <i>Phalaenopsis Orchid Homeobox1</i> (<i>POH1</i>) Functional Gene for Shoot Development in <i>Phalaenopsis</i> Orchid

“…Moreover, KNOX2 also acts as negative regulator of secondary cell wall biosynthesis (Wang et al 2020). ELK Domain acts as a signal for nuclear localization and is included in protein -protein interaction (Nagasaki et al 2001;Ito et al 2002;Nookaraju et al 2022). Homeobox KN Domain acts as transcription factor that is conserved in different plants, which also affects in leaf shape elaboration (Wang & Jiao 2020;Zhang et al 2022).…”

“…Based on ColabFold modelling, we investigate the location of domain, which is KNOX1, KNOX2, ELK Domain and Homeobox KN Domain in 3D structural prediction (Figure 7). KNOX1 and KNOX2 domains are formed into MEINOX domain which is separated by a poorly conserved linker sequence (Nookaraju et al 2022). MEINOX Domain that is located in N-terminus will interact with POX domain from BEL protein (Zhang et al 2021).…”

Current Understanding of the Genetics and Molecular Mechanisms Regulating Wood Formation in Plants

“…After cell wall expansion, SCW deposition occurs. Several excellent reviews have been reported recently on this subject, so please see [ 79 , 80 , 81 , 82 ].…”