Agrobacterium tumefaciens mediated plant transformation is a versatile tool for plant genetic engineering following its discovery nearly half a century ago.Numerous modifications were made in its application to increase efficiency,especially in the recalcitrant major cereals plants.Recent breakthroughs in transformation efficiency continue its role as a mainstream technique in CRISPR/Cas-based genome editing and gene stacking.These modifications led to higher transformation frequency and lower but more stable transgene copies with the capability to revolutionize modern agriculture.In this review,we provide a brief overview of the history of Agrobacterium-mediated plant transformation and focus on the most recent progress to improve the system in both the Agrobacterium and the host recipient.A promising future for transformation in biotechnology and agriculture is predicted.
Agrobacterium-mediated plant transformation is widely used in plant genetic engineering.However,its efficiency is limited by plant immunity against Agrobacterium.Chili pepper(Capsicum annuum L.)is an important vegetable that is recalcitrant to Agrobacterium-mediated transformation.In this work,Agrobacterium was found to induce a strong immune response in pepper,which might be the reason for T-DNA being difficult to express in pepper.An Agrobacterium mutant screen was conducted and a point mutation in the hisI gene was identified due to a weak immune response and enhanced transient expression mediated by this Agrobacterium mutant in pepper leaves.Further genetic analysis revealed that histidine biosynthesis deficiency caused by mutations in many genes of this pathway led to reduced pepper cell death,presumably due to reduced bacterial growth.However,mutation analysis of threonine and tryptophan biosynthesis genes showed that the biosynthesis of different amino acids may play different roles in Agrobacterium growth and stimulating the pepper immune response.The possible application of Agrobacterium amino acid biosynthesis mutations in plant biology was discussed.
Dan LiuShengnan ZhaoJubin WangXi ZhangYingtian DengFeng Li
Jute(Corchorus capsularis L.)is the second most important natural plant fiber source after cotton.However,developing an efficient gene editing system for jute remains a challenge.In this study,the transgenic hairy root system mediated by Agrobacterium rhizogenes strain K599 was developed for Meifeng 4,an elite jute variety widely cultivated in China.The transgenic hairy root system for jute was verified by subcellular localization and bimolecular fluorescence complementation(BiFC)assays.The CHLOROPLASTOS ALTERADOS 1(CcCLA1)gene,which is involved in the development of chloroplasts,was targeted for editing at two sites in Meifeng 4.Based on this hairy root transformation,the gRNA scaffold was placed under the control of cotton ubiquitin GhU6.7 and-GhU6.9 promoters,respectively,to assess the efficiency of gene editing.Results indicated the 50.0%(GhU6.7)and 38.5%(GhU6.9)editing events in the target 2 alleles(gRNA2),but no mutation was detected in the target 1 allele(gRNA1)in transgenic-positive hairy roots.CcCLA1 gene editing at gRNA2 under the control of GhU6.7 in Meifeng 4 was also carried out by Agrobacterium tumefaciens-mediated transformation.Two CcCLA1 mutants were albinic,with a gene editing efficiency of 5.3%.These findings confirm that the CRISPR/Cas9 system,incorporating promoter GhU6.7,can be used as a gene editing tool for jute.
