LBD29-Involved Auxin Signaling Represses NAC Master Regulators and Fiber Wall Biosynthesis

Abstract

NAM, ATAF1/2 and CUC2 (NAC) domain transcription factors function as master switches in regulating secondary cell wall (SCW) biosynthesis in Arabidopsis (Arabidopsis thaliana) stems. Despite the importance of these NACs in fiber development, the upstream signal is still elusive. Using a large-scale mutant screening, we identified a dominant activation-tagging mutant, fiberless-d (fls-d), showing defective SCW development in stem fibers, similar to that of the nac secondary wall thickening promoting factor1-1 (nst1-1)nst3-3 double mutant. Overexpression of LATERAL ORGAN BOUNDARIES DOMAIN29 (LBD29) is responsible for the fls-d mutant phenotypes. By contrast, loss-of-function of LBD29, either in the dominant repression transgenic lines or in the transfer-DNA (T-DNA) insertion mutant lbd29-1, enhanced SCW development in fibers. Genetic analysis and transgenic studies demonstrated LBD29 depends on master regulators in mediating SCW biosynthesis, specifically NAC SECONDARY WALL THICKENING PROMOTING FACTOR1 (NST1), NST2, and NST3. Increasing indole-3-acetic acid (IAA) levels, either in stem tissues above a N-1-naphthylphthalamic acid-treated region or in plants directly sprayed with IAA, inhibits fiber wall thickening. The inhibition effect of naphthylphthalamic acid treatment and exogenous IAA application depends on a known auxin signaling pathway involving AUXIN RESPONSE FACTOR7 (ARF7)/ARF19 and LBD29. These results demonstrate auxin is upstream of LBD29 in repressing NAC master regulators, and therefore shed new light on the regulation of SCW biosynthesis in Arabidopsis.

Comprehensive characterization and gene expression patterns of LBD gene family in Gossypium

“…To be specific, AthLBD16 is involved in instigating the migration of nuclei and in the asymmetric division of lateral root founder cells to promote lateral root initiation (Goh et al 2012). Ath-LBD29 is involved in aspects of auxin signaling that inhibits fiber wall thickening in Arabidopsis stems (Lee et al 2019b). AtLBD20 is a Fusarium oxysporum susceptibility gene that appears to regulate components of jasmonic acid (JA) signalling required for full elicitation of F. oxysporum-and JA-dependent responses (Feng et al 2012).…”

Construction of a Full-Length cDNA Over-Expressing Library to Identify Valuable Genes from Populus tomentosa

“…The regulation of auxin in SCW formation has been widely reported [ 56 , 57 ] and might operate mainly through ASYMMETRIC LEAVES2 (AS2)/LATERAL ORGAN BOUNDARIES DOMAIN (LBD) family proteins. LBD29 , which involves auxin signaling, represses the NAC master regulators and fiber wall biosynthesis [ 58 ], while LBD30/18 genes act downstream of ARF7 and are involved in a positive feedback loop for VND7 expression [ 59 ]. PtoWRKY13 overexpression lines K25/K78 showed stiffer stems and thickened SCWs ( Figure 6 A).…”

Grass secondary cell walls, Brachypodium distachyon as a model for discovery

“…Several LBD family transcription factors, AtLBD15/18/30, can activate the expression of AtVND7 and induce wall thickening and differentiation into tracheary cells (Soyano et al, 2008;Ohashi-Ito et al, 2018). AtLBD29, conversely, is a repressor of stem secondary wall thickening and is activated by the phytohormone auxin (Lee et al, 2019). Repression is also supplied by the MYB G4 clade and are the best characterised in grasses.…”