Regulation of cell wall development in Brachypodium distachyon in vitro as affected by cytokinin and gas exchange

Abstract

Brachypodium distachyon is successfully used as a model grass species. The present study used molecular and chemical approaches to investigate the effects of the addition of the cytokinin 6-benzyladenine (BA) and two levels of gas exchange on the transcriptional regulation of lignin biosynthesis in B. distachyon. It was observed that the control of lignin biosynthesis is affected by both BA and the in vitro gas exchange rate, by sealing the vial with absence or presence of membranes. These observations are supported by anatomical and antioxidant enzyme activity analyses. However, the hyperhydricity caused by BA did not affect cell wall properties in B. distachyon. Interestingly, the CCR1 gene presented 70-fold increase in expression under the effect of BA and without membranes in addition to a significant increase in the peroxidases activity and total lignin content. Treatments with gas exchange showed higher qualitative accumulation of lignin S/G. Lignin pathway genes were transcriptionally coordinated according to the imposed treatment with apparent co-expression. Low expression of these genes was observed in the sealing treatment without membranes, while the opposite was verified in the condition of sealing with two membranes. CESA4 and CESA7 genes responded positively to gas exchange, without altering the cell wall cellulose/lignin ratio in B. distachyon. These results contribute to a better understanding of how cell wall-related gene expression is regulated by exogenous factors, as well as the many possibilities of cell wall manipulation due to its plasticity in adaptive responses.