Agrobacterium-mediated transformation efficiency and grain phenotypes in six indica and japonica rice cultivars

Abstract

Plant transformation and regeneration have been continuously developed over the past four decades. In rice (Oryza sativa L.), Agrobacterium-mediated transformation has high efficiency in japonica and some indica cultivars using mature seeds and immature embryos. However, thesprotocols have low transformation efficiency in the latest indica cultivar that has been developed in South China since 2010. Here, we exploreplant culture regeneration of the high-quality and high-yield indica cultivar Nanguizhan (NGZ) through CRISPR/Cas-based genome editing antraditional overexpression transformations. We compared transformation efficiency in this cultivar to four other widely-used indica cultivars anone japonica cultivar using mature seeds and the gene Grain Size and Number 1 (GSN1) as a case study. We observed universally smaller grain sizin overexpression lines and bigger grain size in gene-editing lines among different cultivars. NGZ phenotypes make it an excellent model iwhich to investigate gene functions. We also examined the single nucleotide polymorphism (SNP) distribution and differences in expressiolevels of regeneration-related genes in calli, possibly revealing the source of NGZ's advantages in Agrobacterium-mediated transformation. Thesresults shed light on the advanced application of NGZ in gene editing and overexpression transformation related to grain improvemencontributing to the 'rice breeding 4.0 era'.