Abstract
Polar auxin transport is involved in multiple aspects of plant development, including root growth, lateral root branching, embryogenesis, and vasculature development. PIN-FORMED (PIN) auxin efflux proteins exhibit asymmetric distribution at the plasma membrane (PM) and collectively play pivotal roles in generating local auxin accumulation, which underlies various auxin-dependent developmental processes. In previous research, it has been revealed that endosomal trafficking components BEN1/BIG5 (ARF GEF) and BEN2/VPS45 (Sec1/Munc 18 protein) function in intracellular trafficking of PIN proteins in Arabidopsis. Mutations in both BEN1 and BEN2 resulted in defects in polar PIN localization, auxin response gradients, and in root architecture. In this study, we have attempted to gain insight into the developmental roles of these trafficking components. We showed that while genetic or pharmacological disturbances of auxin distribution reduced dividing cells in the root tips and resulted in reduced root growth, the same manipulations had only moderate impact on ben1; ben2 double mutants. In addition, we established transgenic lines in which BEN2/VPS45 is expressed under control of tissue-specific promoters and demonstrated that BEN2/VPS45 regulates the intracellular traffic of PIN proteins in cell-autonomous manner, at least in stele and epidermal cells. Furthermore, BEN2/VPS45 rescued the root architecture defects when expressed in internal tissues of ben1; ben2 double mutants. These results corroborate the roles of the endosomal trafficking component BEN2/VPS45 in regulation of auxin-dependent developmental processes, and suggest that BEN2/VPS45 is required for sustainable root growth, most likely through regulation of tip-ward auxin transport through the internal tissues of root.
Highlights
Plant hormone auxin is involved in multiple aspects of plant growth and development, such as embryonic patterning, formation of lateral organs, regulation of organ growth, and tropic responses (Mockaitis and Estelle, 2008; Vanneste and Friml, 2009; Grunewald and Friml, 2010; Zwiewka et al, 2019)
In the wild-type root, relatively small cells with high cell division capacity represent the zone of cell division, or the root meristem, which locates above the quiescent center (QC). ben1 and ben2 single mutants showed similar size of meristem and number of cells in meristematic regions compared with wildtype, ben2 single mutant had a tendency to have slightly short root meristem
We investigated the developmental roles of membrane trafficking components BEN1/BIG5 ARF GEF and BEN2/VPS45 Sec1/Munc18 protein
Summary
Plant hormone auxin is involved in multiple aspects of plant growth and development, such as embryonic patterning, formation of lateral organs, regulation of organ growth, and tropic responses (Mockaitis and Estelle, 2008; Vanneste and Friml, 2009; Grunewald and Friml, 2010; Zwiewka et al, 2019). Root system plays physiological roles such as assimilation and transport of nutrients, and its architecture is an agriculturally important trait. Transport and local accumulation of auxin play pivotal roles in regulating both root growth and branching patterns. Auxin flux is redirected shootwards through the outer layer of tissues such as epidermis, cortex, and lateral root cap. This auxin flow depends on auxin influx and efflux transporters. PIN family auxin-efflux proteins are expressed widely in plant tissues, and some are localized to the plasma membrane (PM) with polar distribution and play a critical role in intercellular transport of auxin. Polar localization of PIN proteins are consistent with the known directionality of auxin transport (Tanaka et al, 2006) and in some cases, manipulation of PIN polar localization causes changes in auxin distribution (Wiśniewska et al, 2006; Huang et al, 2010), indicating the biological significance of the polar localization of PIN proteins in regulating auxin distribution
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