Variation in Growth Rate between Arabidopsis Ecotypes Is Correlated with Cell Division and A-Type Cyclin-Dependent Kinase Activity

Abstract

We used a kinematic analysis to investigate the growth processes responsible for variation in primary root growth between 18 ecotypes of Arabidopsis. Root elongation rate differed 4-fold between the slowest (Landsberg erecta, 71 m h Ϫ1 ) and fastest growing line (Wassilewskija [Ws]; 338 m h Ϫ1 ). This difference was contributed almost equally by variations in mature cortical cell length (84 [Ws]). We found no correlation between mature cell size and endoreduplication, refuting the hypothesis that the two are linked. However, there was a strong correlation between cell production rates and the activity of the cyclin-dependent kinase (CDKA). The level of the protein could explain 32% of the variation in CDKA. Therefore, it is likely that regulators of CDKA, such as cyclins and inhibitors, are also involved. These data provide a functional link between cell cycle regulation and whole-plant growth rate as affected by genetic differences.The rate at which plants grow is an important agronomic trait in cultivated plants, as well as an adaptive trait under natural growth conditions. Therefore, the physiological characteristics associated with fast and slow growth have been extensively investigated (for an overview, see Lambers et al., 1998). They involve the acquisition of growthsupporting substances (photosynthesis and nutrient uptake) and their utilization (anatomy, chemical composition, cell division, and cell expansion). In contrast to the multitude of physiological investigations into the basis of growth rate differences, genetic studies are scarce. Arabidopsis, the model plant for genetic research, has been collected from a wide range of habitats distributed primarily over most of the northern hemisphere. Genetic differences between local populations (commonly called ecotypes, despite that this term does not conform strictly to its ecological definition [Pigliucci, 1998]) are presumably associated with adaptation to the prevailing environmental conditions. Numerous ecotypes were collected by the pioneers of Arabidopsis research and have since been use to investigate a wide range of physiological processes, through comparisons between ecotypes and by genetic mapping using recombinant inbred lines (Alonso-Blanco and Koornneef, 2000). With some notable exceptions (Li et al., 1998), little is published about differences in the rate at which Arabidopsis ecotypes grow when compared under standardized laboratory conditions.There are two complementary views on how root growth is regulated (Silk, 1984). The spatial model describes at what rate division and expansion occur as a function of position along the root axis. Root elongation rate in this model is determined by the size of the growth zone and local rates of expansion. According to this view, cell division merely subdivides cellular space provided by the expansion process. In an alternate manner, a cellular model can be adopted whereby cell production in the meristem drives growth by producing the cells that will subsequently expand to reach a given mature size ...

Geometrical constraints in the scaling relationships between genome size, cell size and cell cycle length in herbaceous plants

“…It is known that a decrease in cell cycle duration is associated with an increase in relative growth rate [47,63], and thus indirectly with photosynthetic rate [64] despite the fact that the relationship need not be straightforward in a population of proliferating cells. These relationships scale up to other plant traits [5] and are fundamental for other biological rates.…”

Multiple Functions of Kip-Related Protein5 Connect Endoreduplication and Cell Elongation

“…Furthermore, the observation that genes associated with plant cell wall organization and with cell elongation (Esmon et al, 2006;Sánchez-Rodríguez et al, 2010) are significantly overrepresented among KRP5 target genes and induced by KRP5 overexpression suggests that KRP5 may regulate simultaneously endoreduplication and cell elongation. In most cases, endoreduplication is associated with cell elongation in plants, as observed in wild-type leaf epidermal cells and etiolated hypocotyls (Traas et al, 1998;Sugimoto-Shirasu and Roberts, 2003), even though cell growth and nuclear DNA content can be uncoupled in some instances (Beemster et al, 2002;Jasinski et al, 2002). Although we cannot rule out the possibility that increased expression of genes related to endocycles or cell elongation is an indirect effect of KRP5 overexpression, the concomitant observation of KRP5 binding to these loci strongly suggests that KRP5 directly regulates their expression.…”

Cellular Responses to Auxin: Division versus Expansion

“…In most Arabidopsis shoot tissues, a positive correlation was reported between the degree of ploidy and cell size. Conversely in roots, such correlation has not been observed however the switch from mitotic cycles to endocycles is coupled with the transition between the root meristem and cell differentiation (Beemster et al 2002;Ishida et al.…”