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Abstract

Growth of leaves and roots are two intimately related processes, in particular through developmental or nutritional clues and their balance is under environmental control. Increases in root/shoot ratio under water or mineral deficit could contribute to the adaptation to poor resource environments. We therefore explored the possibility that this balance and its response to soil water deficit is under genetic control in Arabidopsis. First, the range of variation of this balance was explored in a set of 20 ‘Perlegen’ accessions, using the Phenopsis platform to impose rigorously controlled soil water deficit (Granier et al 2006). Contrasted behaviours of the accessions could be distinguished, based on their degree of shoot growth decrease and root growth maintenance under water deficit. The Bay-0 x Sha RILs population was chosen for QTL analysis from the contrasted response of the parents. In experiments performed in hydroponics or in soil under well watered conditions, most growth QTLs identified were involved in the control of both root and shoot growth. Different variables were thus derived to identify the genetic basis of root or shoot growth (residual of the root shoot relationship, coordinates along PCA axis). A consensus region at the top of chr 3 affecting both primary root length and biomass partitioning was identified and further confirmed using Heterologous Inbred Families. In soil under water deficit, regions controlling root and shoot growth were more loosely related and residual/PCA analysis allowed the identification of regions controlling root or shoot growth or their response to soil water deficit independently. Together, these results show that the strength of the root – shoot relationship is translated at the genetic level, that numerical tools are available to identify regions specifically controlling root growth and that water deficit tend to loosen this relationship suggesting that root growth is more sink limited under water deficit than in normal conditions.