Exploring key cellular processes and candidate genes regulating the primary thickening growth ofMoso underground shoots

Abstract

The primary thickening growth of Moso (Phyllostachys edulis) underground shoots largely determines the culm circumference. However, its developmental mechanisms remain largely unknown. Using an integrated anatomy, mathematics and genomics approach, we systematically studied cellular and molecular mechanisms underlying the growth of Moso underground shoots. We discovered that the growth displayed a spiral pattern and pith played an important role in promoting the primary thickening process of Moso underground shoots and driving the evolution of culms with different sizes among different bamboo species. Different with model plants, the shoot apical meristem (SAM) of Moso is composed of six layers of cells. Comparative transcriptome analysis identified a large number of genes related to the vascular tissue formation that were significantly upregulated in a thick wall variant with narrow pith cavity, mildly spiral growth, and flat and enlarged SAM, including those related to plant hormones and those involved in cell wall development. These results provide a systematic perspective on the primary thickening growth of Moso underground shoots, and support a plausible mechanism resulting in the narrow pith cavity, weak spiral growth but increased vascular bundle of the thick wall Moso.

Morphological dissection and cellular and transcriptome characterizations of bamboo pith cavity formation reveal a pivotal role of genes related to programmed cell death

“…By comparing corpus cell numbers among five bamboo species with different culm sizes, we found that although corpus cells, which develops to pith tissue (Wei et al ., ), were dramatically increased with the increase in culm size, and the ratio of corpus cell number to the square of culm diameter was exponentially decreased with the culm size increase (Figure g–i), somehow demonstrating that the increase in pith cells could not keep pace with the cross‐area increase. Thus, more pith cells should be reassigned to the cross area to fill the gap, highly possibly by decreasing pith cells across the internode.…”

“…Methods for making paraffin section and light microscopy observation were same as described in Wei et al . (). The lengths of over 300 parenchymal cells in each 1‐cm part were measured.…”

“…Unlike the uniform internode shape of other monocotyledon grass species, bamboo internodes display high morphological diversity. For example, the diameter of bamboo culm ranges from about 0.3 cm to over 30 cm (Wei et al, 2017). Our previous work revealed that pith, which has been long ignored by bamboo researchers since it will eventually die to form a cavity and therefore has not been considered valuable, plays an unexpected important role in promoting the primary thickening growth and driving the culm size evolution of bamboo (Wei et al, 2017).…”

“…Although bamboo has been used for many purposes, little is known about its fundamental biological processes (Wei et al, 2017). For a long time, the molecular research of bamboo mainly follows the studies of model plants (Wei et al, 2013).…”

“…For a long time, the molecular research of bamboo mainly follows the studies of model plants (Wei et al, 2013). Recently, with the advancement of next generation sequencing technologies, several studies have reported to explore bamboo transcriptome profiles in several important biological processes such as fast growth, flowering and primary thickening growth (Gao et al, 2014;He et al, 2013;Li et al, 2018;Liu et al, 2012;Peng et al, 2013;Shih et al, 2014;Wei et al, 2017Wei et al, , 2018Zhang et al, 2012). Meanwhile, the genetic transformation system of bamboo has been successfully established (Qiao et al, 2014;Ye et al, 2017), and several groups have made progress in increasing the callus regeneration efficiency, which is important for establishing an efficient transgenic system of bamboo (Wei et al, 2015).…”