Class II Formin BUI1 Plays Important Roles in Actin Organization and Rice Development

A team of researchers, led by Prof. HE Zuhua, from Shanghai Institute of Plant Physiology and Ecology (SIPPE), Shanghai Institutes for Biological Sciences (SIBS), CAS, discovered that a Class II formin BUI1 (BENT UPPERMOST INTERNODE1) plays essential roles in actin cytoskeleton organization and rice development.

Rice productivity is highly associated with its architectural pattern, including plant height, which is attributable mainly to stem internode elongation. The uppermost internode is of particular importance for rice productivity, since the elongation of the uppermost internode promotes panicle emergence and subsequently grain filling. Prof. He’s lab has been devoted to dissecting the rice internode development. In 2006 they identified ELONGATED UPPERMOST INTERNODE (Eui) gene and discovered that Eui controls rice uppermost internode elongation by modulation of the bioactive GA levels (Zhu et al., The Plant Cell, 2006). Now they find that a new gene, BUI1, affects rice internode development by organizing the actin cytoskeleton.

Formins are the key actin nucleation factors involved in many fundamental cellular processes, including cytokinesis, cell motility, and polarity. BUI1 encodes the class II formin FH5. Mutation of BUI1 results in severely disruption of the actin cytoskeleton and consequently inhibition of cell expansion. In collaboration with Dr. HUANG Shanjin’ group from the Institute of Botany, CAS, they dissected the biochemical functions of BUI1 and found that BUI1 could efficiently promote actin filament assembly and actin bundling. Thus, their study identified a rice formin protein BUI1 that regulates de novo actin nucleation and spatial organization of the actin filaments, which are important for proper cell expansion and rice morphogenesis. The identification of BUI1 also reveals a new regulatory mechanism underlying the development of rice internodes,

The research was published online in The Plant Cell on February 9th, 2011.

This work was supported by grants from the Knowledge Innovation Program of the Chinese Academy of Sciences, Ministry of Science and Technology of China, and the National Natural Science Foundation of China. (SIPPE)

AUTHOR CONTACT:
HE Zuhua Ph.D., Professor.
Shanghai Institute of Plant Physiology and Ecology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China.
Telephone: +86-21-54924121; E-mail: zhhe@sibs.ac.cn

The actin cytoskeleton is critical for cell expansion and plant morphogenesis. Formin proteins are important regulators of actin cytoskeleton formation and reorganization. The rice BENT UPPERMOST INTERNODE1 (BUI1) gene encodes a Class II formin that modulates actin organization as well as rice growth and development. This picture shows the emergence process of bui1 panicles against a background of a fluorescent micrograph of filamentous actin (F-actin) in the bui1 flag leaf sheath cells stained with AlexaFluor488-phalloidin. The uppermost internode of bui1 did not grow straightly upward while became bent during heading stage. The actin cytoskeleton was severely disrupted in bui1 cells, with the amount of F-actin decreased and the longitudinal actin cables almost lost.