Ubiquitination and deubiquitination are reversible processes that play crucial roles in regulating organ size in plants. However, information linking deubiquitination and seed size in rice (Oryza sativa) is limited. Here, we characterized a dominant large-grain mutant, large grain1-D (lg1-D), with a 30.8% increase in seed width and a 34.5% increase in 1,000-grain weight relative to the wild type. The lg1-D mutant had more cells oriented in the lateral direction of the spikelet hull compared with the wild type. Mapbased cloning showed that LG1 encodes a constitutively expressed ubiquitin-specific protease15 (OsUBP15) that possesses deubiquitination activity in vitro. Loss-of-function and down-regulated expression of OsUBP15 produced narrower and smaller grains than the control. A set of in vivo experiments indicated that the mutant Osubp15 had enhanced protein stability relative to wild-type OsUBP15. Further experiments verified that OsDA1 directly interacted with OsUBP15. Genetic data indicated that OsUBP15 and GRAIN WIDTH 2 (GW2) were not independent in regulating grain width and size. In summary, we identified OsUBP15 as a positive regulator of grain width and size in rice and provide a promising strategy for improvement of grain yield by pyramiding OsUBP15 and gw2.
Summary
Lesion mimic mutants that exhibit spontaneous hypersensitive response (
HR
)‐like necrotic lesions are ideal experimental systems for elucidating molecular mechanisms involved in plant cell death and defence responses. Here we report identification of a rice lesion mimic mutant,
spotted leaf 35
(
spl35
), and cloning of the causal gene by
TAIL
‐
PCR
strategy.
spl35
exhibited decreased chlorophyll content, higher accumulation of H
2
O
2
, up‐regulated expression of defence‐related marker genes, and enhanced resistance to both fungal and bacterial pathogens of rice. The
SPL
35
gene encodes a novel
CUE
(coupling of ubiquitin conjugation to
ER
degradation) domain‐containing protein that is predominantly localized in cytosol,
ER
and unknown punctate compartment(s).
SPL
35
is constitutively expressed in all organs, and both overexpression and knockdown of
SPL
35
cause the lesion mimic phenotype.
SPL
35 directly interacts with the E2 protein Os
UBC
5a and the coatomer subunit delta proteins Delta‐
COP
1 and Delta‐
COP
2 through the
CUE
domain, and down‐regulation of these interacting proteins also cause development of
HR
‐like lesions resembling those in
spl35
and activation of defence responses, indicating that
SPL
35
may be involved in the ubiquitination and vesicular trafficking pathways. Our findings provide insight into a role of
SPL
35 in regulating cell death and defence response in plants.
Flowering time is an important trait for determining the adaptability of a crop cultivar. A novel heading date regulator, OsHAPL1, interacts with DTH8-Hd1 to negatively regulate flowering time in rice.
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