Diverging cell wall strategies for drought adaptation in two maize inbreds with contrasting lodging resistance.

The plant cell wall is a plastic structure of variable composition that constitutes the first line of defence against environmental challenges. Lodging and drought are two stressful conditions that severely impact maize yield. In a previous work, we characterised the cell walls of two maize inbreds, EA2024 (susceptible) and B73 (resistant) to stalk lodging. Here, we show that drought induces distinct phenotypical, physiological, cell wall, and transcriptional changes in the two inbreds, with B73 exhibiting lower tolerance to this stress than EA2024. In control conditions, EA2024 stalks had higher levels of cellulose, uronic acids and p-coumarate than B73. However, upon drought EA2024 displayed increased levels of arabinose-enriched polymers, such as pectin-arabinans and arabinogalactan proteins, and a decreased lignin content. By contrast, B73 displayed a deeper rearrangement of cell walls upon drought, including modifications in lignin composition (increased S subunits and S/G ratio; decreased H subunits) and an increase of uronic acids. Drought induced more substantial changes in gene expression in B73 compared to EA2024, particularly in cell wall-related genes, that were modulated in an inbred-specific manner. Transcription factor enrichment assays unveiled inbred-specific regulatory networks coordinating cell wall genes expression. Altogether, these findings reveal that B73 and EA2024 inbreds, with opposite stalk-lodging phenotypes, undertake different cell wall modification strategies in response to drought. We propose that the specific cell wall composition conferring lodging resistance to B73, compromises its cell wall plasticity, and renders this inbred more susceptible to drought.

The complete chloroplast genome of Malva wigandii (Alef.) M.F. Ray (Malvaceae, Malvoideae).

The complete chloroplast genome sequence of wild sea mallow Malva wigandii (=Lavatera maritima) was determined and characterized in this study. The genome is 158,162 bp long, containing a pair of inverted repeats regions (IRs) of 25,166 bp, which are separated by a large single-copy region of 86,860 bp and a small single-copy region of 20,970 bp. The sea mallow chloroplast genome has 131 known genes, including 85 protein-coding genes, eight ribosomal RNA genes, and 37 tRNA genes. The phylogenomic analysis showed that M. wigandii forms a cluster with Althaea officinalis with a strong bootstrap support and is sister to sequences belonging to the tribe Gossypieae. All of them are grouped in a lineage with other members of the subfamily Malvoideae. This newly sequenced chloroplast genome sequence provides useful genetic information to explore the origin and evolution of the Mediterranean radiation that gave rise to the generic alliance of Malva.