A Small Guanosine Triphosphate Binding Protein PagRabE1b Promotes Xylem Development in Poplar

Abstract

Rab GTPases are the subfamily of the small guanosine triphosphate (GTP)-binding proteins which participated in the regulation of various biological processes. Recent studies have found that plant Rabs play some specific functions. However, the functions of Rabs in xylem development in trees remain unclear. In this study, functional identification of PagRabE1b in Populus was performed. Quantitative reverse transcription PCR (qRT-PCR) results showed that PagRabE1b was highly accumulated in stems, especially in phloem and xylem tissues. Overexpression of PagRabE1b in poplar enhanced programmed cell death (PCD) and increased the growth rate and the secondary cell wall (SCW) thickness. Quantitative analysis of monosaccharide content showed that various monosaccharides were significantly increased in secondary xylem tissues of the overexpressed lines. Flow cytometry analysis revealed that the number of apoptotic cells in PagRabE1b-OE lines is more than a wild type (WT), which indicated that PagRabE1b may play an important role in PCD. Further studies showed that overexpression of PagRabE1b increased the expression level of genes involved in SCW biosynthesis, PCD, and autophagy. Collectively, the results suggest that PagRabE1b plays a positive role in promoting the xylem development of poplar.

Evidence for poplar PtaPLATZ18 in the regulation of plant growth and vascular tissues development

“…Several other genes have been found to promote cambial activity and xylem development in poplar, together with plant height. For instance, the overexpression of PagRabE1b encoding a small guanosine triphosphate (GTP)-binding protein leads to an increased xylem width by 27-50% and thicker xylem fiber cell walls (Liu et al, 2021). In another study, the overexpression of PagSAG101a induced increased plant height, as well as increased internode number and stem diameter, xylem width (by 5.1-14.7%), and secondary cell wall thickness while opposite phenotypes were observed for PagSAG10a knock-out plants (He et al, 2022).…”

A method for analyzing programmed cell death in xylem development by flow cytometry

“…The isolation of protoplasts from stem-differentiating xylem was carried out as previously described (Lin et al, 2014;Liu et al, 2021) with minor modifications. Briefly, the stem below the 5 th internode was separated into bark and wood and then cut into about 10 cm-long segments.…”

“…To isolate protoplasts from hybrid poplar 84K, we used stems harvested from six 3-month-old 84K plantlets (Figure 2A). We then separated the bark and wood tissues of stems below the 5 th internode and obtained free protoplasts from the differentiating xylem using a previously described digestion method (Lin et al, 2014;Liu et al, 2021). Stem sectioning showed that about 10 layers of differentiating xylem cells were released by enzyme digestion (Figure 2B).…”