The MicroRNA159-Regulated GAMYB-like Genes Inhibit Growth and Promote Programmed Cell Death in Arabidopsis      

Abstract

The microRNA159 (miR159) family represses the conserved GAMYB-like genes that encode R2R3 MYB domain transcription factors that have been implicated in gibberellin (GA) signaling in anthers and germinating seeds. In Arabidopsis (Arabidopsis thaliana), the two major miR159 family members, miR159a and miR159b, are functionally specific for two GAMYB-like genes, MYB33 and MYB65. These transcription factors have been shown to be involved in anther development, but there are differing reports about their role in the promotion of flowering and little is known about their function in seed germination. To understand the function of this pathway, we identified the genes and processes controlled by these GAMYB-like genes. First, we demonstrate that miR159 completely represses MYB33 and MYB65 in vegetative tissues. We show that GA does not release this repression and that these transcription factors are not required for flowering or growth. By contrast, in the absence of miR159, the deregulation of MYB33 and MYB65 in vegetative tissues up-regulates genes that are highly expressed in the aleurone and GA induced during seed germination. Confirming that these genes are GAMYB-like regulated, their expression was reduced in myb33.myb65.myb101 seeds. Aleurone vacuolation, a GA-mediated programmed cell death process required for germination, was impaired in these seeds. Finally, the deregulation of MYB33 and MYB65 in vegetative tissues inhibits growth by reducing cell proliferation. Therefore, we conclude that miR159 acts as a molecular switch, only permitting the expression of GAMYB-like genes in anthers and seeds. In seeds, these transcription factors participate in GA-induced pathways required for aleurone development and death.

Singlet Oxygen-Induced Cell Death in Arabidopsis under High-Light Stress Is Controlled by OXI1 Kinase

“…To sum up, relative to the wild type, high-light stress in oxi1 leaves causes significant down-regulation of photosynthesis, growth processes, and phytohormones, and up-regulation of structural component biogenesis and pigment biosynthesis, all of which are regulated by an interplay of the hormones auxin, ethylene, jasmonic acid, salicylic acid, and gibberellins. Interestingly, in the transcriptomic comparison of oxi1 and the wild type, we noticed the up-regulation in oxi1 leaves of a number of genes proposed to antagonize cell death processes (Cominelli et al, 2000;Danon et al, 2004;Alonso-Peral et al, 2010). This was confirmed by qRT-PCR analyses (Fig.…”

Discovery of precursor and mature microRNAs and their putative gene targets using high-throughput sequencing in pineapple (Ananas comosus var. comosus)

“…For example, the highly abundant miR159 family was found to complement the Ascorbate Peroxidase (APX) transcript, which is not consistent with previous reports. miR159 has been shown to suppress the mRNA levels of GA signaling genes (MYB33 and MYB65) and positive regulators of ABA (MYB33 and MYB101) (Alonso-Peral et al, 2010;Reyes and Chua, 2007;Gubler et al, 1995;Palatnik et al, 2003). Our results suggest that miR159 triggers a different regulatory pathway to reduce GA signaling.…”

The role of small RNAs in vegetative shoot development

“…The altered venation patterns in the miRNA biogenesis hyponastic leaves1 (hyl1) mutant are explained by the reduced miR165 and increased REV expression observed in this mutant [75–77]. Interestingly, miR159a/b double mutants [78] also have a simplified venation pattern and reduced vascular cell number, suggesting that additional miRNA families function in vascular development.…”