Bamboo Flowering from the Perspective of Comparative Genomics and Transcriptomics

Abstract

Bamboos are an important member of the subfamily Bambusoideae, family Poaceae. The plant group exhibits wide variation with respect to the timing (1-120 years) and nature (sporadic vs. gregarious) of flowering among species. Usually flowering in woody bamboos is synchronous across culms growing over a large area, known as gregarious flowering. In many monocarpic bamboos this is followed by mass death and seed setting. While in sporadic flowering an isolated wild clump may flower, set little or no seed and remain alive. Such wide variation in flowering time and extent means that the plant group serves as repositories for genes and expression patterns that are unique to bamboo. Due to the dearth of available genomic and transcriptomic resources, limited studies have been undertaken to identify the potential molecular players in bamboo flowering. The public release of the first bamboo genome sequence Phyllostachys heterocycla, availability of related genomes Brachypodium distachyon and Oryza sativa provide us the opportunity to study this long-standing biological problem in a comparative and functional genomics framework. We identified bamboo genes homologous to those of Oryza and Brachypodium that are involved in established pathways such as vernalization, photoperiod, autonomous, and hormonal regulation of flowering. Additionally, we investigated triggers like stress (drought), physiological maturity and micro RNAs that may play crucial roles in flowering. We also analyzed available transcriptome datasets of different bamboo species to identify genes and their involvement in bamboo flowering. Finally, we summarize potential research hurdles that need to be addressed in future research.

Keywords: bamboo; drought; flowering pathways; future research; genes; plant age.

Figure 1

Important vegetative and floral developmental stages of B. tulda. (A) External morphology of nodal vegetative bud (~0.6 × 0.7 cm in dimension); (B) Longitudinal section (L.S.) of vegetative bud. The shoot apical meristem (SAM) is dome shaped (marked with arrow); (C) External morphology of an early stage inflorescence bud (~0.3 × 0.3 cm in dimension); (D) LS of the early stage inflorescence bud having triangular inflorescence meristem (marked with arrow); (E) External morphology of middle stage inflorescence bud (~0.8 × 0.5 cm in dimension); (F) LS of middle stage inflorescence bud showing differentiated floral primordia (marked with arrow); (G) External morphology of late stage inflorescence bud (~1.2 × 0.6 cm in dimension); (H) LS of late stage inflorescence bud having differentiated anther primordia (marked with arrow).