The Simultaneous Repression of CCR and CAD, Two Enzymes of the Lignin Biosynthetic Pathway, Results in Sterility and Dwarfism in Arabidopsis thaliana

Abstract

Cinnamoyl CoA reductase (CCR) and cinnamyl alcohol dehydrogenase (CAD) catalyze the last steps of monolignol biosynthesis. In Arabidopsis, one CCR gene (CCR1, At1g15950) and two CAD genes (CAD C At3g19450 and CAD D At4g34230) are involved in this pathway. A triple cad c cad d ccr1 mutant, named ccc, was obtained. This mutant displays a severe dwarf phenotype and male sterility. The lignin content in ccc mature stems is reduced to 50% of the wild-type level. In addition, stem lignin structure is severely affected, as shown by the dramatic enrichment in resistant inter-unit bonds and incorporation into the polymer of monolignol precursors such as coniferaldehyde, sinapaldehyde, and ferulic acid. Male sterility is due to the lack of lignification in the anther endothecium, which causes the failure of anther dehiscence and of pollen release. The ccc hypolignified stems accumulate higher amounts of flavonol glycosides, sinapoyl malate and feruloyl malate, which suggests a redirection of the phenolic pathway. Therefore, the absence of CAD and CCR, key enzymes of the monolignol pathway, has more severe consequences on the phenotype than the individual absence of each of them. Induction of another CCR (CCR2, At1g80820) and another CAD (CAD1, At4g39330) does not compensate the absence of the main CCR and CAD activities. This lack of CCR and CAD activities not only impacts lignification, but also severely affects the development of the plants. These consequences must be carefully considered when trying to reduce the lignin content of plants in order to facilitate the lignocellulose-to-bioethanol conversion process.

Transcription Factor MYB26 Is Key to Spatial Specificity in Anther Secondary Thickening Formation

“…Given that the NST1 and NST2 genes are responsible for induction of secondary thickening biosynthesis genes and appear to be downstream and regulated by MYB26, we tried to complement the myb26 mutation by overexpression of NST1 and NST2 using the CaMV35S promoter. Secondary thickening in anthers was observed using a combined stain of ethidium bromide, which indicates lignified cells (red fluorescence) and acridine orange, which stains lignified walls with a drop in fluorescence for nonlignified walls (green fluorescence; Stockert et al, 1984;Yang et al, 2007;Thévenin et al, 2011). As previously reported, we observed that the myb26 mutant failed to develop endothecium thickening (Fig.…”

“…The composition of the thickening appears to be critical for dehiscence, since the triple ccc mutant, which is defective for cinnamoyl CoA reductase1, cinnamyl alcohol dehydrogenase c and cinnamyl alcohol dehydrogenase d, has hypolignified stems and accumulates higher amounts of flavonol glycosides, sinapoyl malate. and feruloyl malate, has abnormal endothecium thickening, and is male sterile (Thévenin et al, 2011).…”

Cell wall modifications triggered by the down-regulation of Coumarate 3-hydroxylase-1 in maize

“…These plants presented growth reduction, over-accumulation of anthocyanins and sterility. These phenotypic traits are similar to the ones described in other heavily C3H-repressed [19,21,23] or lignin-down regulated plants [72,73]. 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 …”

Casparian strip diffusion barrier in Arabidopsis is made of a lignin polymer without suberin

“…This process is very challenging because of the high redundancy within the enzyme families involved (21). However, once a sufficient number of biosynthetic mutants were combined, we expectedly observed pleiotropic germination and growth defects.…”