Abstract
In many tree species especially the rooting-recalcitrant woody perennials, the adventitious root (AR) in the juvenile phase can be easily induced by exogenous auxin, but AR formation becomes recalcitrant in the adult phase. Also, it is reported that the γ-aminobutyric acid (GABA) inhibits primary root growth in Arabidopsis and the AR formation in poplar (Populus ssp). So far, how GABA affects or is affected by the ontogenetic phase or auxin remains unclear. Here, we used an apple rootstock, Malus xiaojinensis, and tobacco (Nicotiana benthamiana) to investigate this question. We first analyzed the content of GABA, the activity of GABA synthetic enzyme GAD, and the expression of the coding gene MxGADs, respectively, in leafy cuttings of juvenile and adult phase. Next, the effect of exogenous GABA on AR formation was examined in in vitro shoots of M. xiaojinensis and tobacco. Interestingly, significant and consistent increases in GABA concentration, GAD activity, and expression of MxGAD genes in response to exogenous indole butyric acid (IBA) were detected in adult-phase cuttings, but not in juvenile-phase cuttings. Exogenous GABA application inhibited the AR formation by delaying rooting time and reducing root number and the total root length in in vitro shoots of both M. xiaojinensis and tobacco. The expression of MxPIN members increased in response to IBA application, but these changes were restrained by the addition of GABA. These results indicate that both the loss of juvenility and IBA are required to trigger GABA accumulation. GABA may affect the AR formation as a co-actor by inhibiting polar auxin transport. Together, these findings facilitate the understanding of the regulatory network among GABA, juvenility, and auxin signaling on the AR formation.
Highlights
Introduction γAminobutyric acid (GABA), a non-protein amino acid, is synthesized from glutamate (Glu), which is catalyzed by the enzyme glutamate decarboxylase (GAD)
From the RNA-seq data, five MxGAD genes exhibited differential expression between M. xiaojinensis (Mx-A) and Mx-J cuttings. These genes were designated as MxGAD1-1, MxGAD1-2, MxGAD2, MxGAD3/4, and MxGAD5 according to the phylogenesis with Arabidopsis (Fig. S1)
In the absence of indole butyric acid (IBA), no considerable variations were detected in GABA content, GAD enzyme activity, and MxGADs expression between Mx-J and Mx-A
Summary
Introduction γAminobutyric acid (GABA), a non-protein amino acid, is synthesized from glutamate (Glu), which is catalyzed by the enzyme glutamate decarboxylase (GAD). GABA is conserved from bacteria to animals, and was extensively studied in plants over half-a-century (Bouche et al 2003; Bach et al 2009; Podlesakova et al 2019). GABA is an important natural molecule produced in almost all living organisms, whereas its content is usually higher in plants than that in animals (Ramos-Ruiz et al 2018; Al-Taher and Nemzer 2019). GABA accumulates in plants under abiotic stressful condition or undergoing senescence (Han et al 2012; Zarei et al 2015; Oh et al 2019). The GABA content in apple (Malus domestica) increased during cold storage or controlled atmosphere storage (low temperature and low oxygen) (Lum et al 2016; Luo et al 2018; Brikis et al 2018). Under controlled atmosphere storage condition, the source of GABA is believed to
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
