Mechanisms Of Soybean ERECTA Responsive To Shade Stress

Maize-soybean relay strip intercropping system is an improved intercropping system compared to the traditional ways of intercropping and not only does it ensure food security, but also improves land equivalent ratio and provides shade to soybean through maize canopy which can cause changes in light quality and intensity. This shade can affect the growth and developmental stages of soybean increasing lodging and exhibition of shade avoidance syndrome resulting to low yield. All of which necessitated the research on molecular mechanism of shade avoidance. From the study,1. For shade treatment, Nan 032-4, Arabidopsis Col-0 and er mutants showed similar shade avoidance syndrome, which included elongation of hypocotyl, and reduction in leaf area. The er mutants was relatively insensitive to shade environment and hypocotyl elongation was a good indicator of shade avoidance reaction.2. Nan 032-4 leaf photosynthetic rate, intercellular CO2 concentration, stomatal conductance and transpiration rate also decreased significantly. The photosynthesis intensity of Nan 032-4 also reduced in the shade treatment.3. Four paralogous ERECTA genes in soybean were realised as a result of duplication events. Soybean ERECTA genes family, GmERa (Glyma04g05912), GmERb (Glyma06g05900), GmERc (Glyma14g11220) and GmERd (Glyma17g34380) were divided into two branches. RT-PCR studies showed that the expression of ERECTA genes in Arabidopsis tissues and the transcript levels were high in the Shoot Apical Meristem.4. RT-PCR studies showed a high expression level of soybean ERECTA homologous receptor kinase in shade treatment. The expression of ERECTA gene in Arabidopsis Col-0 also increased significantly. Signifying that, soybean ERECTA homologous receptor kinases were involved in the shade avoidance treatment5. During the cloning of CDS sequence of GmERa and promoters of GmERa, GmERb, GmERc, GmERd by Gateway cloning technology, PBASTA-35S-GmERa-GFP, pBASTA-GmERap-GUS, pBASTA-GmERbp-GUS, pBASTA-GmERcp-GUS and pBASTA-GmERdp-GUS were constructed. The recombinant plasmid were transformed into Agrobacterium GV3101, disseminated Arabidopsis Col-0 and er and transgenic plants were identified by spraying Basta and RT-PCR.6. Transgenic plants containing GmERa was able to restore the phenotype of er mutants:the leaf area and petiole length were larger than that of the wild type Col-0 and also hypocotyl and petiole elongation of transgenic plants were significant.7. The hypocotyl of homozygote Arabidopsis phyb and er mutant was elongated, but shorter than that of the phyb mutant in shade avoidance treatment. At different concentrations of GA3, PIC, ACC,24-epiBL, PAC and NPA of hormone treatment, GA3, PIC, ACC and 24-epiBL promoted hypocotyl elongation of Col-0, er,phyb and er phyb. GA3 significantly promoted hypocotyl elongation of er, and there was no difference compared to Col-0 in shade treatment. But PAC, NPA significantly inhibited the elongation of the hypocotyls in shade treatment. The study showed that ERECTA stimulated the elongation of the hypocotyl which was partly dependent on PHYB and interacted with plant hormones in shade treatment.8. After GUS staining of Arabidopsis transgenic plants, expression of ERECTA gene increased in leaf, hypocotyl and petiole. Signifying that ERECTA gene in Arabidopsis thaliana was involve in the shade avoidance response, and also at the different tissue expression levels. After GA3, PIC, ACC,24-epiBL hormone treatment, expression of AtER, AtERLl and AtERL2 increased in shade treatment and the expression of GmERs also increased in the hypocotyl, petiole, and the Shoot Apical Meristem. Similar to Arabidopsis ERECTA gene family, expression of GmERs was different in different tissues9. RT-PCR studies showed an increase in GmGA30Xl, GmGA20OX1 and GmIAA29 expression and decrease in GmGAlOX1 expression. Real-time qPCR indicated an increase level of AtIAA29, AtGA3OX1, AtGA20OX1, AtPIL1, AtPIF4, AtSAUR68, AtRGA1 and decreased level in AtGA2OX1 and AtGAl. Indicated that, GA and IAA signaling pathway related genes of soybean and Arabidopsis were involved in the regulation of shade avoidance.Studies on the morphology, physiology and gene expression of soybean and Arabidopsis indicated that, ERECTA receptor kinases respond to the low ratio of red and far red light are dependent on phytochrome B. When light signal was transerred to the phytochrome B in cytoplasm. Phytochrome B changed from Pfr type to Pr type, which entered the nucleus and interacted with transcription factors, and then started the GA and IAA genes expression, which finally promoted hypocotyl elongation.