No abstract

It is well studied that potassium (K +) deficiency induced aberrant growth and development of plant and altered the expression of protein-coding genes. However, there are not too many systematic investigations on root development affected by K + deficiency, and there is no report on miRNA expression during K + deficiency in wheat. In this study, we found that K + deficiency significantly affected wheat seedling growth and development, evidenced by reduced plant biomass and small plant size. In wheat cultivar AK-58, upground shoots were more sensitive to K + deficiency than roots. K + deficiency did not significantly affect root vitality but affected root development, including root branching, root area, and root size. K + deficiency delayed seminal root emergence but enhanced seminal root elongation, total root length, and correspondingly total root surface area. K + deficiency also affected root and leaf respiration at the early exposure stage, but these effects were not observed at the later stage. One potential mechanism causing K + deficiency impacts is microRNAs (miRNAs), one important class of small regulatory RNAs. K + deficiency induced the aberrant expression of miRNAs and their targets, which further affected plant growth, development, and response to abiotic stresses, including K + deficiency. Thereby, this positive root adaption to K + deficiency is likely associated with the miRNA-involved regulation of root development.

The mechanism of miRNA-mediated root growth and development in response to nutrient deficiency in peanut (Arachis hypogaea L.) is still unclear. In the present study, we found that both nitrogen (N) and potassium (K) deficiency resulted in a significant reduction in plant growth, as indicated by the significantly decreased dry weight of both shoot and root tissues under N or K deficiency. Both N and K deficiency significantly reduced the root length, root surface area, root volume, root vitality, and weakened root respiration, as indicated by the reduced O2 consuming rate. N deficiency significantly decreased primary root length and lateral root number, which might be associated with the upregulation of miR160, miR167, miR393, and miR396, and the downregulation of AFB3 and GRF. The primary and lateral root responses to K deficiency were opposite to that of the N deficiency condition. The upregulated miR156, miR390, NAC4, ARF2, and AFB3, and the downregulated miR160, miR164, miR393, and SPL10 may have contributed to the growth of primary roots and lateral roots under K deficiency. Overall, roots responded differently to the N or K deficiency stresses in peanuts, potentially due to the miRNA-mediated pathway and mechanism.

Based on our previous study, cereal crop wheat (Triticum aestivum L.) could be infected by rhizobia Azorhizobium caulinodans ORS571, and form para-nodules with the induction of 2.4-dichlorophenoxyacetic acid, a common plant growth regulator. To enhance this infection and the potential agricultural application, we compared six different infection methods (Direct seed dip; Seed germination dip; Pruned-root dip; Foliar spray; Circum-soil dip; Seed dip and circum-soil dip) for achieving the high efficient infection of A. caulinodans into wheat plants by employing a green fluorescent protein (gfp)-labeled Azorhizobium caulinodans strain ORS571. With proper methods, copious rhizobia could enter the interior and promote the growth of wheat to the hilt. Circum-soil dip was proved to be the most efficient method, seed germination dip and pruned-root dip is the last recommended to infect wheat, seed germination dip and seed dip and circum-soil dip showed better effects on plant growth, pruned-root dip did not show too much effect on plant growth. This study laid the foundation for understanding the interaction between rhizobia and cereal crops and the growth-promoting function of rhizobia.