ORIGINAL ARTICLE Architectural analysis of root system and phytohormone biosynthetic genes expression in wheat (Triticum aestivum L.) inoculated with Penicillium oxalicum P.K. Tiwari, J. Yadav, A.K. Singh, R. Srivastava, A.K. Srivastava, P.K. Sahu , A.K. Srivastava and A.K. Saxena ICAR-National Bureau of Agriculturally Important Microorganisms, Maunath Bhanjan, Uttar Pradesh, India Significance and Impact of the Study; Although the impact of microbes on plant growth promotion and root architecture has been widely examined using bacteria, the role of fungi is much less studied. Here, we examined the effect of a potential fungal plant growth promoter Penicillium oxalicum T4 on root architecture and growth of wheat seedlings. Confocal scanning laser micrographs and scanning electron micrographs indicted profuse colonization in wheat roots and induction of root hairs, respec- tively. Furthermore, P. oxalicum T4 was shown to modulate the expression of host genes related to root growth and development. Overall, P. oxalicum T4 was found to hold promise as a potential microbial formulation for boosting wheat growth. Keywords Penicillium, rhizosphere, root architecture, symbiosis, transcriptional regulation. Correspondence Pramod K. Sahu and Alok K. Srivastava, ICAR-National Bureau of Agriculturally Impor- tant Microorganisms, Maunath Bhanjan- 275 103, Uttar Pradesh, India. E-mail: aloksrivastva@gmail.com; pramod15589@gmail.com, 2022/LAMICRO-2022-0111.R2: received 25 February 2022, revised 16 June 2022 and accepted 23 August 2022 doi:10.1111/lam.13827 Abstract In this study, a fungal plant growth promoter Penicillium oxalicum T4 isolated from non-rhizosphere soil of Arunachal Pradesh, India, was screened for different plant growth promoting traits in a gnotobiotic study. Though inoculation improved the overall growth of the plants, critical differences were observed in root architecture. Confocal Laser Scanning Microscope, Scanning electron microscope and the stereo microscopic study showed that inoculated wheat plants could develop profuse root hairs as compared to control. Root scanning indicated improvement in cumulative root length, root area, root volume, number of forks, links, crossings, and other parameters. A confocal scanning laser microscope indicated signs of endophytic colonization in wheat roots. Gene expression studies revealed that inoculation of T4 modulated the genes affecting root hair development. Significant differences were marked in the expression levels of TaRSL4, TaEXPB1, TaEXPB23, PIN-FORMED protein, kaurene oxidase, lipoxygenase, ACC synthase, ACC oxidase, 9-cis- epoxycarotenoid dioxygenase, and ABA 8 0 -hydroxylase genes. These genes contribute to early plant development and ultimately to biomass accumulation and yield. The results suggested that P. oxalicum T4 has potential for growth promotion in wheat and perhaps also in other cereals. Introduction Climate change has posed severe challenges to sustainable crop production for the increasing global population with declining resources (Reynolds 2010). Efforts are being taken for developing innovative techniques for climate- resilient crop production (Westermann et al. 2018; Singh et al. 2021). One of the promising strategies is the ame- lioration of adverse effects through microbial inoculation. Although plants are sessile, they have active interaction with the surrounding microbial world, which aids growth under adverse conditions. Many reports suggest the cardi- nal roles of these microbes in improving plant growth, nutrient acquisition, nutrient fortification and biotic and abiotic stress tolerance (Srivastava et al. 2001; Meena et al. 2017; Sahu et al. 2021). Fungal agents are widely explored for the biocontrol of plant pathogens. In con- trast, the role of growth-promotion attributes has only Letters in Applied Microbiology 75, 1596--1606 © 2022 Society for Applied Microbiology. 1596 Letters in Applied Microbiology ISSN 0266-8254 Downloaded from https://academic.oup.com/lambio/article/75/6/1596/6989413 by guest on 20 January 2023