Latent infection of Vigna unguiculata with seed-borne bean common mosaic virus modulates plant growth and may contribute to establishing mutualistic symbiosis between virus and host plant

Hideki Takahashi ^1* Nan Xu ¹ Yoshinori Kanayama ¹ Midori Tabara ² Atsushi Takeda ² Toshiyuki Fukuhara ³ Shuhei Miyashita ¹

• ¹ Graduate School of Agricultural Science, Tohoku University, Sendai, Japan
• ² College of Life Sciences, Ritsumeikan University, Kusatsu, Japan
• ³ Department of Applied Biological Science, Faculty of Agriculture, Tokyo University of Agriculture and Technology, Kyoto, Kyōto, Japan

In evaluating the germination and growth of the seed resources of 322 cultivars of cowpea (Vigna unguiculata), we found the development of yellow symptoms on ~50% of the cotyledons of 10 cultivars. RNA-seq analysis of total RNA extracted from symptomatic cotyledons indicated that the 10 cultivars were infected with bean common mosaic virus (Potyvirus phaseovulgaris, BCMV), which is a member of the family Potyviridae and was able to seed-transmit to progeny plants. One of the BCMV isolates identified in the 10 cultivars was BCMV(Vu06), which was infected to cultivar #6.During the growth of BCMV(Vu06)-infected cowpea plants, there were no systemic symptoms in newly developing leaves, but the virus coat protein was detected in both leaves and flowers. Thus, the cowpea cultivar #6 plant was latently infected with BCMV(Vu06). There was no significant difference in the dry matter weight of the above-ground parts of the plant between BCMV(Vu06)-latently infected and noninfected plants. However, BCMV(Vu06)-latently infected plants had late flower and bud formation and longer life but slightly lower seed yield compared with non-infected plants. The 1000-seed weight and germination frequency of the seeds harvested from infected plants were the same as those of non-infected plants. Taken together, latent infection of cultivar #6 with BCMV(Vu6) modulates the balance between vegetative and reproductive plant growth, and the longer lifespan of BCMV(Vu06)-latently infected plants may provide an advantage for its survivability over generations. BCMV(Vu06) and cowpea cultivar #6 might have established a mutual symbiotic relationship during their interaction.