Molecular Mechanism Of Arabidopsis LecRk-8A Involved In Seed Size Determination

Receptor like kinases(RLKs), a class of important plant proteins sensing and transducing extracellular signal into cell, have irreplaceable function in plant growth, development, biotic and abiotic stress responses. Lectin like receptor kinases(Lec RKs) family is a calss of RLKs, most of them play significant roles in plant immunity and stress response, as well as hormone signaling. However, several members affect the development of pollen, suggesting that Lec RKs might have potential roles in plant growth. As a member of Lec RKs, Lec RK-8A has typical signal peptide and transmembrane domain which generally consist in Lec RKs, indicating that Lec RK-8A might be localized on cell membrance. The e FP browser results show that Lec RK-8A has the highest expression in integument of developing seed at 6-7 stage, suggesting that Lec RK-8A might have a potential role in seed development. The embryo, endosperm and integument growth, leading to seed development and mature jointly, is influenced by phytohormone, such as brassinolide(BR), abscisic acid(ABA), cytokinin(CTK) and auxin(IAA). It is also affected by ubiquitin pathway and other signals. Dysplasia in any of them may affect seed shape, size, as well as nutrient content. After comparing seeds of Lec RK-8A mutants, overexpression line and wild type, we found that mutants had smaller seeds, while overexpression line seeds are much larger than wild type. By using differential interference contrast microscopy, we found that Lec RK-8A determined seed size before the stage of globular embryo. Seeds from reciprocal cross between mutants and wild type had similar size with their female parent, suggesting that Lec RK-8A tents to express in seed coat, and the expression is affected by female parent. To investigate the sub-cellular localization of Lec RK-8A and the gene expression pattern, 35S::Lec RK-8A-GFP transient expression vector and Pro Lec RK-8A::GUS vector were structured. By RT-PCR, the expression difference between mutants and wild type about gene function in seed development was analyzed. Result showed that Lec RK-8A promoted expression of MINI3 via a way independent of IKU1 and SHB1, and suppressed AP2 expression slightly. Lec RK-8A, suppressed by exogenous ABA, was found to improve germination rate under salt stress and promote expression of ABI5, which might compensate seeds diminution caused by the afunction of Lec RK-8A through ABI5-SHB1 pathway. In conclusion, Lec RK-8A might combine with ABA signal pathway tightly to regulate seed development. The above results show that Lec RK-8A has incredible roles in enlargement of seed size and acceleration of embryo development. It is likely to have a great reference value in increasing grain yield.