Roles of Aquaporins in Setaria viridis Stem Development and Sugar Storage

Abstract

Setaria viridis is a C4 grass used as a model for bioenergy feedstocks. The elongating internodes in developing S. viridis stems grow from an intercalary meristem at the base, and progress acropetally toward fully expanded cells that store sugar. During stem development and maturation, water flow is a driver of cell expansion and sugar delivery. As aquaporin proteins are implicated in regulating water flow, we analyzed elongating and mature internode transcriptomes to identify putative aquaporin encoding genes that had particularly high transcript levels during the distinct stages of internode cell expansion and maturation. We observed that SvPIP2;1 was highly expressed in internode regions undergoing cell expansion, and SvNIP2;2 was highly expressed in mature sugar accumulating regions. Gene co-expression analysis revealed SvNIP2;2 expression was highly correlated with the expression of five putative sugar transporters expressed in the S. viridis internode. To explore the function of the proteins encoded by SvPIP2;1 and SvNIP2;2, we expressed them in Xenopus laevis oocytes and tested their permeability to water. SvPIP2;1 and SvNIP2;2 functioned as water channels in X. laevis oocytes and their permeability was gated by pH. Our results indicate that SvPIP2;1 may function as a water channel in developing stems undergoing cell expansion and SvNIP2;2 is a candidate for retrieving water and possibly a yet to be determined solute from mature internodes. Future research will investigate whether changing the function of these proteins influences stem growth and sugar yield in S. viridis.

Whole-Genome and Expression Analyses of Bamboo Aquaporin Genes Reveal Their Functions Involved in Maintaining Diurnal Water Balance in Bamboo Shoots

“…PePIP1;6 , PePIP2;7 , and PeTIP1;3 were co-expressed with four types of sugar transporter genes, including PLT , SUC / SUT , SWEET , and pGlcT . These results were similar to those co-expressed genes involved in water and sugar transport-related processes in the developing grass stems of Setaria viridis [ 35 ], which indicated that the PeAQP s might participate in the regulation of bamboo shoot growth through water and sugar transport, which would require further studies.…”

The potential of resilient carbon dynamics for stabilizing crop reproductive development and productivity during heat stress

“…This is more critical for perennial species, because it will allow essential non‐foliar structures to avoid senescence while not limiting reproductive development and productivity. Additionally, in bioenergy grasses, the accumulation of stem sugars is essential for productivity (Feltus & Vandenbrink, 2012), such that enhancing export to stems has been proposed as a target trait for improvement in these crops (McGaughey et al, 2016). As we have previously discussed, however, sugar transport activity is impaired by heat stress, thereby highlighting the importance of stem and ear photosynthesis in such situations.…”

Versatile Roles of Aquaporins in Plant Growth and Development

“…Both OsTIP1;1 and OsTIP2;2 have water channel activity when expressed in yeast cells. The transcription levels of SvPIP2;1 are also very high in the elongating stem in Setaria viridis [ 90 ] ( Figure S1 ). Based on these observations, it is plausible that these PIPs, SIPs and especially TIPs as water transporters function in hypocotyl and stem growth.…”