The Pea DELLA Proteins LA and CRY Are Important Regulators of Gibberellin Synthesis and Root Growth  

Abstract

The theory that bioactive gibberellins (GAs) act as inhibitors of inhibitors of plant growth was based originally on the slender pea (Pisum sativum) mutant (genotype la cry-s), but the molecular nature of this mutant has remained obscure. Here we show that the genes LA and CRY encode DELLA proteins, previously characterized in other species (Arabidopsis [Arabidopsis thaliana] and several grasses) as repressors of growth, which are destabilized by GAs. Mutations la and cry-s encode nonfunctional proteins, accounting for the fact that la cry-s plants are extremely elongated, or slender. We use the la and cry-s mutations to show that in roots, DELLA proteins effectively promote the expression of GA synthesis genes, as well as inhibit elongation. We show also that one of the DELLAregulated genes is a second member of the pea GA 3-oxidase family, and that this gene appears to play a major role in pea roots.It is well known that primary root growth is strongly influenced by the plant hormone GA (Davies, 2004). For example, the application of bioactive GA to roots treated with the growth inhibitor ancymidol completely restored growth to that of the untreated plants (Tanimoto, 1991). Yaxley et al. (2001) established the importance of GAs for root growth in peas (Pisum sativum) by using a variety of GA-deficient mutant plants. In the na-1 mutant, for example, root GA 1 levels, and root elongation, were significantly reduced compared with wild-type plants, and when the GA 1 content was restored to wild-type levels, so too was root elongation.The GAs act by destabilizing the growth inhibitory DELLA proteins (Peng et al., 1997;Harberd et al., 1998;Silverstone et al., 2001;Alvey and Harberd, 2005). In other words, GA acts as an ''inhibitor of an inhibitor '' (Harberd et al., 1998). Interestingly, there is also evidence that DELLA proteins promote the biosynthesis of active GAs. For example, in the Arabidopsis (Arabidopsis thaliana) DELLA mutant rga, the expression of the biosynthesis gene GA4 is reduced, indicating that high DELLA protein levels are associated with an up-regulation of GA synthesis genes (Silverstone et al., 2001 (Silverstone et al., 1998;Gubler et al., 2002). However, the available evidence indicates greater redundancy in dicots compared with monocots (Ikeda et al., 2001;Thomas and Hedden, 2006). There have been five DELLA genes isolated from Arabidopsis (GAI, RGA, RGL1, RGL2, and RGL3), yet only one in rice (SLR1), barley (SLN1), and maize (Zea mays; D8; Peng et al., 1997Peng et al., , 1999Silverstone et al., 1998;Ikeda et al., 2001;Chandler et al., 2002;Gubler et al., 2002), with the possibility of another DELLA gene in maize (D9; accession no. ABI84225). It should be noted, however, that DELLAs have been studied in fewer dicot model species than in monocot species. To date, DELLA-encoding genes from pea have not been reported, even though observations on the slender phenotype of pea triggered the early suggestion that GA acts an inhibitor of an inhibitor (Brian, 1957). The elongated slender phenotype, con...

Light Regulation of Gibberellin Biosynthesis in Pea Is Mediated through the COP1/HY5 Pathway

“…The pronounced effect of long1 on the length of the first two internodes is most similar to that of the constitutive GA-response double DELLA mutant la cry-s (Potts et al, 1985;Weston et al, 2008) and the GA-overproducing sln mutant, which has a mutation in the GA catabolism gene GA2ox1 (Reid et al, 1992;Lester et al, 1999) (Figures 1A and 1B). By contrast, the phyB mutant, although equivalently elongated over later internodes, has only a weak effect on elongation of early internodes (Figures 1A and (A), (B), and (E) Phenotypes of elongated mutant seedlings under glasshouse conditions.…”

“…The long1-1 point mutation was converted into a derived CAPS marker, introducing a diagnostic NcoI site. Molecular markers for detection of the phyA-1, phyB-5, la-1, and cry-s mutations have been described previously (Platten et al, 2005;Weston et al, 2008). Details of all primers are provided in Supplemental Table 1 online.…”

“…In various crosses, we observed tight linkage between LONG1 and the ST locus and weaker linkage of LONG1 with other group III classical markers B and DNE. This indicated a position near the LA gene (Weeden et al, 1998), recently shown to encode a GA-signaling DELLA protein (Weston et al, 2008), and we therefore considered the possibility that long1 and la might be allelic. However, the presence of several recombinants in a cross segregating for long1 and la excluded this possibility and suggested a LA-LONG1 distance of ;4 centimorgans.…”

“…The la monogenic mutation has no phenotype in an otherwise wild-type background, and potential allelism of long1 and la was therefore assessed in the F2, F3, and F4 progeny of a cross between long1 and the la cry double mutant. Briefly, F3 families segregating for all three mutations were genotyped for la and cry mutations using molecular markers (Weston et al, 2008), and recombinants were identified as elongated plants that that were heterozygous for the la mutation (implying a long1 long1 LA la genotype and the contribution of a recombinant long1 la gamete) or as plants with a wildtype phenotype that were homozygous LA LA (implying the presence of at least one wild-type LONG1 allele and recombinant LONG1 LA gamete). The genetic distance between LONG1 and LA was estimated from this segregation data using JOINMAP software (van Ooijen, 2006).…”

Reply: Interaction between Brassinosteroids and Gibberellins: Synthesis or Signaling? In Arabidopsis, Both!

“…In particular, the DELLAs contribute to the feedback control of GA production because transcript levels of GA20ox and GA3ox genes are low in mutants lacking DELLAs but are strongly elevated in plants containing stabilized DELLA forms (Dill et al, 2001;Zentella et al, 2007;Weston et al, 2008). Interestingly, this feedback control appears to be inactive in BR mutants because despite low levels of bioactive GA, GA20ox and GA3ox expression is not induced (Unterholzner et al, 2015).…”