Cell-to-cell communication precisely controls the creation of new organs during reproductive growth. However, the sensor molecules that mediate developmental signals in monocot plants are poorly understood. Here, we report that DWARF AND RUNTISH SPIKELET1 (DRUS1) and DRUS2, two closely related receptor-like kinases (RLKs), redundantly control reproductive growth and development in rice (). A double knockout mutant, but not either single mutant, showed extreme dwarfism and barren inflorescences that harbored sterile spikelets. The gibberellin pathway was not impaired in this mutant. A phenotypic comparison of mutants expressing different amounts of DRUS1 and 2 revealed that reproductive growth requires a threshold level of DRUS1/2 proteins. DRUS1 and 2 maintain cell viability by repressing protease-mediated cell degradation and likely by affecting sugar utilization or conversion. In the later stages of anther development, survival of the endothecium requires DRUS1/2, which may stimulate expression of the UDP-glucose pyrophosphorylase gene and starch biosynthesis in pollen. Unlike their ortholog FERONIA, DRUS1 and 2 mediate a fundamental signaling process that is essential for cell survival and represents a novel biological function for the CrRLK1L RLK subfamily.

SUMMARYThe palea and lemma are unique organs in grass plants that form a protective barrier around the floral organs and developing kernel. The interlocking of the palea and lemma is critical for maintaining fertility and seed yield in rice; however, the molecules that control the interlocking structure remain largely unknown. Here, we showed that when OsCR4 mRNA expression was knocked down in rice by RNA interference, the palea and lemma separated at later spikelet stages and gradually turned brown after heading, resulting in the severe interruption of pistil pollination and damage to the development of embryo and endosperm, with defects in aleurone. The irregular architecture of the palea and lemma was caused by tumour-like cell growth in the outer epidermis and wart-like cell masses in the inner epidermis. These abnormal cells showed discontinuous cuticles and uneven cell walls, leading to organ self-fusion that distorted the interlocking structures. Additionally, the faster leakage of chlorophyll, reduced silica content and elevated accumulation of anthocyanin in the palea and lemma indicated a lesion in the protective barrier, which also impaired seed quality. OsCR4 is an active receptor-like kinase associated with the membrane fraction. An analysis of promoter::GUS reporter plants showed that OsCR4 is specifically expressed in the epidermal cells of paleas and lemmas. Together, these results suggest that OsCR4 plays an essential role in maintaining the interlocking of the palea and lemma by promoting epidermal cell differentiation.

Receptor-like kinases (RLKs) play important roles in multiple aspects of plant growth and development. As a member of the TNFR-like RLK subfamily, rice Crinkly4 (OsCR4) functions mainly in epidermal cell differentiation in many organs. Here we show that in addition to its essential role in epidermal cell differentiation in the palea and lemma, OsCR4 positively regulates rice culm elongation, similar to maize CR4. Although OsCR4 is an active kinase, like CR4 in maize and ACR4 in Arabidopsis, the conserved amino acid K532 in OsCR4 is not essential for its kinase activity in vitro. Whether other conserved amino acids are required for its kinase activity and the relationship between its activity and function in plant development remain to be investigated.

No abstract

No abstract