B-box (BBX) proteins play important roles in plant growth regulation and development including photomorphogenesis, photoperiodic regulation of flowering, and responses to biotic and abiotic stresses. In the present study we retrieved total 131 BBX members from five Poaceae species including 36 from maize, 30 from rice, 24 from sorghum, 22 from stiff brome, and 19 from Millet. All the BBX genes were grouped into five subfamilies on the basis of their phylogenetic relationships and structural features. The expression profiles of 12 OsBBX genes in different tissues were evaluated through qRT-PCR, and we found that most rice BBX members showed high expression level in the heading stage compared to seedling and booting stages. The expression of OsBBX1, OsBBX2, OsBBX8, OsBBX19, and OsBBX24 was strongly induced by abiotic stresses such as drought, cold and salt stresses. Furthermore, the expression of OsBBX2, OsBBX7, OsBBX17, OsBBX19, and OsBBX24 genes was up-regulated under GA, SA and MeJA hormones at different time points. Similarly, the transcripts level of OsBBX1, OsBBX7, OsBBX8, OsBBX17, and OsBBX19 genes were significantly affected by heavy metals such as Fe, Ni, Cr and Cd. Change in the expression pattern of BBX members in response to abiotic, hormone and heavy metal stresses signifies their potential roles in plant growth and development and in response to multivariate stresses. The findings suggest that BBX genes could be used as potential genetic markers for the plants, particularly in functional analysis and determining their roles under multivariate stresses.

Carbohydrate-binding malectin/malectin-like domain-containing proteins (CBMs) are a recently identified protein subfamily of lectins that participates various functional bioprocesses in the animal, bacterial, and plant kingdoms. However, little is known the roles of CBMs in rice development and stress response. In this study, OsCBM1, which encodes a protein containing only one malectin-like domain, was cloned and characterized. OsCBM1 is localized in both the endoplasmic reticulum and plasma membrane. Its transcripts are dominantly expressed in leaves and could be significantly stimulated by a number of phytohormone applications and abiotic stress treatments. Overexpression of OsCBM1 increased drought tolerance and reactive oxygen species production in rice, whereas the knockdown of the gene decreased them. OsCBM1 physically interacts with OsRbohA, a NADPH oxidase, and the expression of OsCBM1 in osrbohA, an OsRbohA-knockout mutant, is significantly downregulated under both normal growth and drought stress conditions. Meanwhile, OsCBM1 can also physically interacts with OsRacGEF1, a specific guanine nucleotide exchange factor for the Rop/Rac GTPase OsRac1, and transient coexpression of OsCBM1 with OaRacGEF1 significantly enhanced ROS production. Further transcriptome analysis showed that multiple signaling regulatory mechanisms are involved in the OsCBM1-mediated processes. All these results suggest that OsCBM1 participates in NADPH oxidase-mediated ROS production by interacting with OsRbohA and OsRacGEF1, contributing to drought stress tolerance of rice. Multiple signaling pathways are likely involved in the OsCBM1-mediated stress tolerance in rice.