Combining Enhanced Root and Shoot Growth Reveals Cross Talk between Pathways That Control Plant Organ Size in Arabidopsis      

Abstract

Functionally distinct Arabidopsis (Arabidopsis thaliana) genes that positively affect root or shoot growth when ectopically expressed were combined to explore the feasibility of enhanced biomass production. Enhanced root growth resulting from cytokinin deficiency was obtained by overexpressing CYTOKININ OXIDASE/DEHYDROGENASE3 (CKX3) under the control of the root-specific PYK10 promoter. Plants harboring the PYK10-CKX3 construct were crossed with four different transgenic lines showing enhanced leaf growth. For all combinations, the phenotypic traits of the individual lines could be combined, resulting in an overall growth increase. Unexpectedly, three out of four combinations had more than additive effects. Both leaf and root growth were synergistically enhanced in plants ectopically expressing CKX3 and BRASSINOSTEROID INSENSI-TIVE1, indicating cross talk between cytokinins and brassinosteroids. In agreement, treatment of PYK10-CKX3 plants with brassinolide resulted in a dramatic increase in lateral root growth that could not be observed in wild-type plants. Coexpression of CKX3 and the GROWTH-REGULATING FACTOR5 (GRF5) antagonized the effects of GRF5 overexpression, revealing an interplay between cytokinins and GRF5 during leaf cell proliferation. The combined overexpression of CKX3 and GIBBER-ELLIN 20-OXIDASE1 led to a synergistic increase in leaf growth, suggesting an antagonistic growth control by cytokinins and gibberellins. Only additive effects on root and shoot growth were visible in plants ectopically expressing both CKX3 and ARABIDOPSIS VACUOLAR PYROPHOSPHATASE1, hinting at an independent action mode. Our results show new interactions and contribute to the molecular and physiological understanding of biomass production at the whole plant level.As the world population is estimated to grow to 9.2 billion people by 2050, the availability of plant-derived products has to increase drastically to meet the needs not only for food, feed, and fiber but also for bioenergy and other industrial applications (Borlaug, 2007). In the future, less arable land will be available while more crops will need to be produced. To lower the negative impact on the environment, increasing plant biomass production on existing agricultural land will diminish the demand for new crop acreage (Edgerton, 2009). Whereas traditional breeding combined with improved agronomical practices will not keep up with the increasing global demands, biotechnology can help serve this purpose (Borlaug, 2007). Marker-assisted breeding and introduction of transgenic traits for biotic and abiotic stress resistance have proven to increase crop gain (Eathington et al., 2007;Edgerton, 2009). Furthermore, improving yield by modulating endogenous molecular pathways will be an important feature of the next generation of biotech crops.The introduction of multiple transgenes has become widely adopted (Naqvi et al., 2010); for example, three carotenoid biosynthesis genes enable provitamin A production in transgenic rice (Oryza sativa) cv Golden Rice (Ye et al., 2...

Root growth and productivity of conventional and herbicide-tolerant canola in contrasting environments

“…A significant increase in volume and root surface was noted in Guarapuava, compared to Passo Fundo, differing from the results obtained by Vercruyssen et al (2011), which concluded that the phenotypical effects in root and growth of the shoots are mostly regulated by changes in genetic competence in optimal environment conditions and not by the source/drain regulation.…”

Brassinosteroids Antagonize Gibberellin- and Salicylate-Mediated Root Immunity in Rice

“…In compliance with this concept, there is ample evidence demonstrating extensive interplay between BR and other small-molecule hormones (Zhang et al, 2009). For example, BR modulates the biosynthesis of ET (Hansen et al, 2009) and intimately interacts with cytokinins and auxin in regulating various developmental processes (Goda et al, 2004;Vert et al, 2008;Peleg et al, 2011;Vercruyssen et al, 2011). Moreover, several microarray experiments and more recent biochemical approaches point to cross talk between BR and ABA and JA signaling pathways, respectively (Goda et al, 2002;Nemhauser et al, 2006;Zhang et al, 2009).…”

ANGUSTIFOLIA3 Binds to SWI/SNF Chromatin Remodeling Complexes to Regulate Transcription during Arabidopsis Leaf Development

“…qRT-PCR was performed as previously described (Vercruyssen et al, 2011). In short, LightCycler 480 SYBR Green I Master (Roche) was used, and relative expression levels were determined by the method of Livak and Schmittgen (2001).…”