Loose Plant Architecture1, an INDETERMINATE DOMAIN Protein Involved in Shoot Gravitropism, Regulates Plant Architecture in Rice  

Abstract

Tiller angle and leaf angle are two important components of rice (Oryza sativa) plant architecture that play a crucial role in determining grain yield. Here, we report the cloning and characterization of the Loose Plant Architecture1 (LPA1) gene in rice, the functional ortholog of the AtIDD15/SHOOT GRAVITROPISM5 (SGR5) gene in Arabidopsis (Arabidopsis thaliana). LPA1 regulates tiller angle and leaf angle by controlling the adaxial growth of tiller node and lamina joint. LPA1 was also found to affect shoot gravitropism. Expression pattern analysis suggested that LPA1 influences plant architecture by affecting the gravitropism of leaf sheath pulvinus and lamina joint. However, LPA1 only influences gravity perception or signal transduction in coleoptile gravitropism by regulating the sedimentation rate of amyloplasts, distinct from the actions of LAZY1. LPA1 encodes a plant-specific INDETERMINATE DOMAIN protein and defines a novel subfamily of 28 INDETERMINATE DOMAIN proteins with several unique conserved features. LPA1 is localized in the nucleus and functions as an active transcriptional repressor, an activity mainly conferred by a conserved ethylene response factor-associated amphiphilic repression-like motif. Further analysis suggests that LPA1 participates in a complicated transcriptional and protein interaction network and has evolved novel functions distinct from SGR5. This study not only facilitates the understanding of gravitropism mechanisms but also generates a useful genetic material for rice breeding.Rice (Oryza sativa) is the staple food for more than half of the world's population. In the past 50 years, the green revolution and the use of heterosis have greatly improved rice yields (Peng et al., 2008). However, because of the increasing demand for rice production, food security can still be a serious problem. Thus, new elite varieties that can produce much higher grain yields need to be developed, and ideal plant architecture (ideotype) breeding has been shown to be the most promising strategy in tropical areas (Khush, 2005). Rice plant architecture is mainly determined by plant height and tiller and panicle morphology, of which tiller angle and leaf angle are two important agronomic traits.Tiller angle, defined as the angle between the main culm and its side tillers, has long attracted the attention of breeders due to the significant contribution of this trait to plant architecture .

DELLA protein functions as a transcriptional activator through the DNA binding of the INDETERMINATE DOMAIN family proteins

“…For example, a rice ZmID1 homolog, OsID1, promotes flowering, as does AtIDD8 (NUTCRACKER; NUC) (17,(27)(28)(29). Later, a functional role in gravitropism was reported for AtIDD15 (SHOOT GRAVITROPISM 5; SGR5) and OsIDD14 (LOOSE PLANT ARCHITECTURE1; LPA1) (30)(31)(32). To date, only one report has described physical interactions of AtIDD1 (ENHYDROUS; ENY) with each of the five DELLA members (33).…”

Maize LAZY1 Mediates Shoot Gravitropism and Inflorescence Development through Regulating Auxin Transport, Auxin Signaling, and Light Response

“…The root responds in the same manner in the columella cells of the root cap (Blancaflor et al, 1998). Some regulators are shared between shoot and root gravitropism, while others are specific to the shoot gravity response (Masson et al, 2002;Morita, 2010;Strohm et al, 2012;Wu et al, 2013). The classical shoot gravitropism mutant phenotype "lazy" has been identified in many plants, including lazy-1 and lazy-2 in tomato (Solanum lycopersicum; Roberts, 1984;Gaiser and Lomax, 1993), lazy in rice (Jones and Adair, 1938), lazy serpentina in barley (Hordeum vulgare; Suge and Türkan, 1991), Two bait constructs expressed full-length ZmLA1 (LA-BD) or truncated ZmLA1 with deletion of residues 1 to 100 (LAΔ100-BD) fused with the DNA-binding domain (BD).…”

“…S1B), implying that the agravitropism phenotype is specific to shoots. Furthermore, unlike traditional gravitropic mutants (Li et al, 2007;Wu et al, 2013), the ps1 mutants displayed no noticeable changes in leaf angle compared with wild-type plants (Table I).…”

Strigolactones regulate rice tiller angle by attenuating shoot gravitropism through inhibiting auxin biosynthesis

“…In the past years, several genes that determine rice tiller angle have been cloned and characterized (5)(6)(7)(8)(9). Some of them, for example LA1 and LPA1, are involved in shoot gravitropism and thus regulate tiller/branch angle in different plant species (5,9,32,33), indicating that shoot gravitropism is the key component dictating the proper positioning of shoot branches. Although the asymmetric distribution of auxin has long been regarded as the main factor that affects shoot gravitropism, the underlying molecular mechanism still remains to be elucidated.…”

“…Several genes controlling the tiller angle have been identified previously in rice, including LAZY1 (LA1), TILLER ANGLE CONTROL1 (TAC1), PROSTRATE GROWTH1 (PROG1), and LOOSE PLANT ARCHITECTURE1 (LPA1) (5)(6)(7)(8)(9). Among these genes, LA1 and LPA1 are reported to regulate tiller angle through shoot gravitropism.…”