The rice germin-like protein OsGLP1 participates in acclimation to UV-B radiation.

Exposure to ultraviolet B radiation (UV-B) stress can have serious effects on the growth and development of plants. Germin-like proteins (GLPs) may be involved in different abiotic and biotic stress responses in different plants, but little is known about the role of GLPs in UV-B stress response and acclimation in plants. In the present study, knockout of GLP 8-14 (OsGLP1) using the CRISPR/Cas9 system resulted in mutant rice (Oryza sativa L.) plants (herein called glp1) that exhibited UV-B-dependent formation of lesion mimic in leaves. Moreover, glp1 grown under solar radiation (including UV-B) showed decreased plant height and increased leaf angle, but we observed no significant differences in phenotypes between wild-type (WT) plants and glp1 grown under artificial light lacking UV-B. Fv/Fm, Y (II) and the expression of many genes, based on RNA-seq analysis, related to photosynthesis were also only reduced in glp1, but not in WT, after transfer from a growth cabinet illuminated with artificial white light lacking UV-B to growth under natural sunlight. The genes-associated with flavonoid metabolism as well as UV resistance locus 8 (OsUVR8), phytochrome interacting factor-like 15-like (OsPIF3), pyridoxal 5'-phosphate synthase subunit PDX1.2 (OsPDX1.2), deoxyribodipyrimidine photolyase (OsPHR), and deoxyribodipyrimidine photolyase family protein-like (OsPHRL) exhibited lower expression levels, while higher expression levels of mitogen-activated protein kinase 5-like (OsMPK3), mitogen-activated protein kinase 13-like (OsMPK13), and transcription factor MYB4-like (OsMYB4) were observed in glp1 than in WT after transfer from a growth cabinet illuminated with artificial white light to growth under natural sunlight. Therefore, mutations in OsGLP1 resulted in rice plants more sensitive to UV-B and reduced expression of some genes for UV-B protection, suggesting that OsGLP1 is involved in acclimation to UV-B radiation.

Overexpression of OsIAAGLU reveals a role for IAA-glucose conjugation in modulating rice plant architecture.

KEY MESSAGE: OsIAAGLU could catalyze the reaction of IAA with glucose to generate IAA-glucose. Overexpression of OsIAAGLU in rice resulted in altered rice shoot architecture and root gravitropism. The distribution and levels of indole-3-acetic acid (IAA) within plant tissues are well known to play vital roles in plant growth and development. An important mechanism of regulating free IAA levels in monocots is formation of IAA ester conjugates. In this study, a cytosol-localized protein encoded by the rice gene of indole-3-acetic acid glucosyltransferase (OsIAAGLU) was found to catalyze the reaction of free IAA with glucose to generate IAA-glucose. Expression of OsIAAGLU could be induced by IAA and NAA. The number of tillers and leaf angle was significantly increased with a concomitant decrease in plant height and panicle length in the transgenic rice lines overexpressing OsIAAGLU compared to the wild-type (WT) plants. Phenotypes of iaaglu mutants constructed using the CRISPR/Cas9 system had no obvious differences with WT plants. Furthermore, overexpression of OsIAAGLU resulted in reduced sensitivity to IAA/NAA and altered gravitropic response of the roots in the transgenic plants. Free IAA contents in the leaves, root tips, and lamina joint of OsIAAGLU-overexpressing transgenic lines were lower than those of WT plants. These results support that OsIAAGLU could play a regulatory role in IAA homeostasis and rice architecture.