EXO70C2 Is a Key Regulatory Factor for Optimal Tip Growth of Pollen

EXO70A2 is critical for the exocyst complex function in Arabidopsis pollen

“…An analogous situation, i.e. the presence of pollen-optimized paralogs, has been documented in the case of SEC3, SEC15 and EXO84 exocyst subunits in Arabidopsis, where SEC3a, SEC15a and EXO84a are pollen-specific, while their siblings are active in the sporophyte (Bloch et al, 2016;Synek et al, 2017;Batystová et al, submitted). Analogically to our observation that the artificial EXO70A2 expression in the sporophyte could complement the sporophytic defects of exo70a1 mutants, SEC15a, the main SEC15 isoform in pollen, could substitute for the function of SEC15b in the sporophyte, although SEC15a and SEC15b share mere 47% sequence identity at the protein level (Batystová et al, submitted).…”

“…First, EXO70A2 is the closest paralog to EXO70A1 -the main EXO70 isoform in the Arabidopsis sporophyte -and these two share 72% sequence identity at the protein level. Second, EXO70A2 also physically interacted with three other exocyst subunits (SEC3a, SEC10b and EXO84b), similarly to EXO70A1 (Hála et al, 2008;Fendrych et al, 2010;Synek et al, 2017). Third, the expression patterns of EXO70A1 and EXO70A2 alternate between the sporophyte-specific and pollenspecific, respectively.…”

“…The exocyst, first described in yeasts and mammals, consists of eight subunits -Sec3, Sec5, Sec6, Sec8, Sec10, Sec15, Exo70, and Exo84 (TerBush et al, 1996;Guo et al, 1999), with Sec3 and Exo70 generally believed to be responsible for targeting the complex to the PM, while the other subunits form the core of the complex (Boyd et al, 2004;He et al, 2007;Pleskot et al, 2015). Plant genomes encode all exocyst subunits (Cvrčková et al, 2001;Eliáš et al 2003) that form a functional complex (Hála et al, 2008;Fendrych et al, 2010) and engage in cellular processes requiring targeted secretion, including root hair and pollen tube elongation (Cole et al, 2005;Synek et al, 2006;Hála et al, 2008;Synek et al, 2017), cytokinesis (Fendrych et al, 2010;Rybak et al, 2014), secondary cell wall deposition in trichomes and during xylem development (Kulich et al, 2015;Kubátová et al, 2019;Vukašinović et al, 2017), localized deposition of seed coat pectins (Kulich et al, 2010), transport of PIN auxin carriers to the PM , and response to pathogens (Pečenková et al, 2011;Sabol et al, 2017). Viable mutants of A. thaliana defective in exocyst subunits (sec8-4, sec15b, exo70a1, exo84b) exhibit dwarfish growth with pleiotropic developmental defects (Cole et al, 2005;Synek et al, 2006;Hála et al, 2008;Fendrych et al, 2010;Batystová et al, submitted).…”

“…This plant-specific multiplicity of EXO70 suggests not only functional specialization in different plant tissues or cell types, but also a presence of several variants of the exocyst complex in the same cell (Žárský et al, 2013). Indeed, some EXO70.2 and EXO70.3 clade members contribute to conventional secretion in specific cell types, while several other isoforms acquired functions outside the conventional exocytosis pathway, acting in exocyst subcomplexes or even independently of the exocyst complex in some cases Kulich et al, 2015;Zhang et al, 2015;Hong et al, 2016;Pečenková et al, 2017;Synek et al, 2017). On the contrary, the Arabidopsis EXO70.1 isoform EXO70A1, highly expressed in most sporophytic tissues, is the main housekeeping EXO70 subunit participating in conventional exocytosis (Synek et al, 2006;Fendrych et al, 2010;Drdová et al, 2013).…”

Monitoring Polysaccharide Dynamics in the Plant Cell Wall

“…When used at low concentrations, PI enables imaging in Arabidopsis root hairs and pollen tubes without altering cell growth (Rounds et al, 2011). Mutant pollen tubes with impaired exocytosis show repetitive bursts of growing tips at cell wall regions that accumulate PI-stained demethylesterified HG (Synek et al, 2017). Alternatively, sparsely methylated HG can be labeled in real time with fluorescently tagged COS (Table II), and the specificity of this labeling was tested using carbohydrate microarrays (Mravec et al, 2014).…”