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The maize low-lignin mutant F2bm3 shows pleiotropic effects on photosynthetic and cell wall metabolisms in response to chilling
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International audience. Maize (Zea mays L.) is one of the major crops in the world and is highly sensitive to lowtemperature due to its tropical origin. Chilling may particularly affect maize during earlyseedling growth by altering physiological processes including photosynthesis and cellwall properties, leading to biomass reduction. Changes in photosynthetic and cell wallmetabolisms were investigated during a long chilling exposure in a low-lignin maizemutant, brown midrib3 (bm3), which contains a null-mutation in the gene encodingcaffeic acid O-methyltransferase (COMT). Wild-type F2 plants and the near-isogenic F2bm3 mutant were grown during 60 days with a day/night temperature regime of15°C/11°C in a greenhouse. Photosynthetic pigments, non-structural sugars, cell wallsugars, lignin, cell wall bound hydroxycinnamic acids (HCA) contents andphenylpropanoid pathway enzyme activities were determined when the 4th leaf had fullyemerged. Results showed that the plants were smaller in response to chilling and thiswas more pronounced in the mutant. However, both genotypes showed good vigor.F2bm3 contained a two-fold increase in the level of chlorophyll a and accumulatedzeaxanthin in response to chilling compared to F2, indicating an alternativephotoprotection mechanism. Unlike the wild-type F2 line, the starch content wasreduced in the F2bm3 mutant and the sucrose/starch partitioning was increased inF2bm3. Few changes in the non-cellulosic cell wall sugars composition could bedetected, except a higher degree of substitution of glucuronoarabinoxylan and a highercontent of β-glucan in both lines in response to chilling. The lignin content in leaves didnot significantly change. But the concentration of HCAs was increased in F2bm3 while itdecreased in F2. Furthermore, the concentration of esterified ferulic acid (FA) wasgreater in F2bm3, suggesting a higher degree of cross-linking between GAX and FAunder chilling treatment. Thus, the increase in arabinose substitution on the xylanbackbone and the abundance of HCA in F2bm3 could increase cell wall extensibility,thereby maintaining the hydration status of the cell wall in response to chilling. Inaddition, the higher concentrations of HCA and chlorophyll observed in F2bm3 suggestthat HCAs could function as photoprotectors, thus enhancing chilling tolerance.
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