A Dianthovirus RNA1-like RNA (DR1L RNA, 4486 nucleotides in length) was found in grassy stunt-diseased rice plants together with Rice grassy stunt virus (RGSV). DR1L RNA has characteristics common to Dianthovirus RNA1 such as (1) presence of a GGAUUUUUAG potential shifty-heptanucleotide at the end of the 5'-proximal ORF, which encodes a 35-kDa protein, followed by a 77-nucleotide sequence capable of forming a stem-loop structure for an efficient--1 frameshift to express the downstream region in a 96-kDa putative replicase protein, (2) presence of nearly identical 17-nucleotide sequences in the 5'-terminal region and in a region upstream of an ORF encoding a 28-kDa, putative capsid protein (CP), and (3) near identity of the 3'-terminal 20 nucleotides to those of Dianthovirus RNAs. Western blot analysis using an antiserum against the C-terminal domain of the putative CP and RT-PCR analysis using primers specific to DR1L RNA of fractions after sucrose density gradient centrifugation of RGSV nucleoproteins indicated that DR1L RNA is associated with the 28-kDa putative CP but not with the 36-kDa RGSV CP. Two additional ORFs for 15-kDa and 33-kDa proteins were present in DR1L RNA although their expression in plants and functions are not known.