The Lotus japonicus AFB6 Gene Is Involved in the Auxin Dependent Root Developmental Program

Abstract

Auxin is essential for root development, and its regulatory action is exerted at different steps from perception of the hormone up to transcriptional regulation of target genes. In legume plants there is an overlap between the developmental programs governing lateral root and N2-fixing nodule organogenesis, the latter induced as the result of the symbiotic interaction with rhizobia. Here we report the characterization of a member of the L. japonicus TIR1/AFB auxin receptor family, LjAFB6. A preferential expression of the LjAFB6 gene in the aerial portion of L. japonicus plants was observed. Significant regulation of the expression was not observed during the symbiotic interaction with Mesorhizobium loti and the nodule organogenesis process. In roots, the LjAFB6 expression was induced in response to nitrate supply and was mainly localized in the meristematic regions of both primary and lateral roots. The phenotypic analyses conducted on two independent null mutants indicated a specialized role in the control of primary and lateral root elongation processes in response to auxin, whereas no involvement in the nodulation process was found. We also report the involvement of LjAFB6 in the hypocotyl elongation process and in the control of the expression profile of an auxin-responsive gene.

Identification of potential Auxin Response Candidate genes for soybean rapid canopy coverage through comparative evolution and expression analysis

“…Although the auxin signaling pathway is well studied and known to play an important role in plant growth, development, and architecture in A. thaliana, little is known about auxin’s roles in legumes (Li and Chen, 2023; Salehin et al, 2015) outside root and nodule development (Breakspear et al 2014; Wang et al 2015; Cai et al 2017; Nadzieja et al 2018; Schiessl et al 2019; Wang et al 2019; Gao et al 2021; Rogato et al, 2021; Goto et al 2022; Li and Chen, 2023) and shoot height/dwarfing. Auxin’s gene regulatory genes are composed of an extensive number of genes for each TIR1/AFB , ARF , and Aux/IAA families in both A. thaliana and G. max .…”

“…Auxin’s gene regulatory genes are composed of an extensive number of genes for each TIR1/AFB , ARF , and Aux/IAA families in both A. thaliana and G. max . These auxin genes work together in a tissue-dependent manner (Piya et al ., 2014) conducting shoot development and rosette area (Vernoux et al ., 2011; Salehin et al ., 2015; Prigge et al ., 2020), organ primordia, as well as cell fate (Rogato et al ., 2021; Salehin et al ., 2015; Parry et al ., 2009) in plants. Therefore, auxin’s mechanism of regulation is a great candidate for plant breeding programs (Li and Chen, 2023).…”

“…Clade II, consists of AFB2/AFB3-like proteins and also contains four G. max representatives but does not contain any G. soja and only one representative each from M. truncatula and L. japonicus (Figure 2). Clade III, is comprised by the AFB6-like proteins, Medtr8g098695.2 and Lj4g0012889.1 defined in Rogato et al (2021), and, according to Parry et al (2009), this clade was lost during the evolution of the Brassicaceae (A. thaliana family) and Poaceae families. We identified two G. max AFB6 orthologs.…”

TIR1/AFB proteins: Active players in abiotic and biotic stress signaling

“…TIR1/AFB family members were also found to be key players in response to nitrate in other plant species. In Lotus japonicus , expression of LjAFB6 is induced in response to exogenous nitrate ( Rogato et al., 2021 ). These studies indicate that AFB3 in Arabidopsis and LjAFB6 in L. japonicus are potentially involved in plant responses to stress caused by excessive nitrate.…”

“…While most abiotic and biotic stresses suppress the expression of TIR1/AFB family members, some stresses can induce their expression. In L. japonicus , LjAFB6 expression increased by 2.5-fold after nitrate treatment ( Rogato et al., 2021 ). Arabidopsis AFB3 was also found to be positively regulated by nitrate addition ( Vidal et al., 2010 ; Vidal et al., 2013 ).…”