<i>Agrobacterium</i>-mediated transformation efficiency and grain phenotypes in six <i>indica</i> and <i>japonica</i> rice cultivars

Plant transformation and regeneration have been continuously developed for 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, these protocols have low transformation efficiency in the latest indica cultivar that has been developed in South China since 2010. Here, we explored plant culture regeneration of the high-quality and high-yield indica cultivar Nanguizhan (NGZ) through CRISPR/Cas-based genome editing and traditional overexpression transformations. We compared transformation efficiency in this cultivar to four other widely-used indica cultivars and one japonica cultivar using mature seeds and the gene Grain Size and Number 1 (GSN1) as a case study. We observed universe smaller grain size in overexpression lines and bigger grain size in gene-editing lines among different cultivars. NGZ phenotypes make it an excellent model in which to investigate gene functions. We also examined the single nucleotide polymorphism (SNP) distribution and differences in expression levels of regeneration-related genes in calli, possibly revealing the source of NGZ's advantages in Agrobacterium-mediated transformation. These results shed light on the advanced application of NGZ in gene editing and overexpression transformation related to grain improvement, contributing to the "rice breeding 4.0 era".