SummaryA chimeric mitochondrial DNA (mtDNA) configuration of the cytoplasmic male-sterile (cms) sorghum line ISl112C includes a 321 bp open reading frame designated orfl07, encoding a predicted polypeptide product of 11.85 kDa. The open reading frame, similar to several other genes associated with cms, consists of amino-terminal sequences derived from an obligate gene. Unlike other examples to date, however, the carboxy-terminal sequences are highly similar to the carboxy terminus of an open reading frame implicated in cms of rice, orf79. The amino-terminal 31 residues of orfl07 are 84% similar to atp9, and the carboxy-terminal 49 residues are 57% identical and 80% similar to the carboxy terminus of orf79. Transcripts of off107 are edited, with four C-to-U changes that alter amino acids. Sorghum lines partially or fully restored to fertility exhibit a high-efficiency internal-orfl07 transcript processing activity, precluding abundant wholelength transcripts, while male-sterile lines exhibit only a trace of the activity. Previous data on the abundance of a 12 kDa in organello-synthesized polypeptide in male-sterile versus male-fertile lines are correlated with differential o#107 transcript processing activity of these lines. Examinations of backcross and F 2 lines suggest a gametophytic mode of restoration, and indicate that enhanced transcript processing activity is necessary, but not sufficient, to restore full fertility. These novel observations indicate that mitochondrial open reading frames associated with cms

Sequencing of sorghum mitochondrial atp6 cDNA clones revealed 19 C-to-U transcript editing events within a 756 bp-conserved core gene; three were silent and 16 resulted in 15 amino acid changes. Only one edit, which was silent, was found in the 381 bp amino-extension to the core gene. Eleven of the 15 changed amino acids were identical with or else represented conservative changes compared to yeast atp6. Editing of a CAA codon to TAA truncates the carboxy-terminus to a position identical to that of yeast. The frequency of editing at sites which change amino acids was very high in contrast to partial editing at silent, third base, sites.

During pollen maturation, single-celled microspores undergo a rapid phase of starch biosynthesis, presumably from sucrose stored in the vacuoles. Very little is known about the genes and the intracellular controls that regulate the sucrose → starch pathway in such microspores. We show here RNA profiles in sorghum microspores during the transition from vacuolated microspore to immature pollen at two specific stages of pollen development: early, showing little or no detectable starch, and late, when pollen are active in starch-filling. We have also examined two near-isogenic cytoplasmic male sterile lines that retain fully turgid immature pollen until the starch-filling stage, but remain starch-deficient, and ultimately form inviable pollen. Using maize cDNA clones, both temporal and genotypic differences were observed in the expression profiles of four metabolic genes (soluble or vacuolar invertase, Ivr2; sucrose synthase, Sus1; phosphoglucomutase, Pgm; and a subunit of ADPG pyrophosphorylase, Bt2), two similar metabolic regulatory genes (Grf1 and Grf2, encoding 14-3-3 proteins) and a transcription factor, ZmMADS1. Western blot analyses were conducted to visualize sucrose synthase, SS2; AGPase, BT2 and the GRF (14-3-3) proteins. Temporal differences of both a qualitative and quantitative nature were observed in all three proteins in both male-fertile and male-sterile lines. We suggest that these changes in gene expression may result from increased and decreased sink strengths and associated changes in carbohydrate metabolism in starch-filled (fertile) and starch-deficient (sterile) pollen, respectively.

Insect pests cause significant global agricultural damage and lead to major financial and environmental costs. Crops contain intrinsic defenses to protect themselves from such pests, including a wide array of specialized secondary metabolite-based defense chemicals. These chemicals can be induced upon attack (phytoalexins) or are constitutive (phytoanticipins), and can have a direct impact on the pests or be used indirectly to attract their natural enemies. They form part of a global arms race between the crops and their insect pests, with the insects developing methods of suppression, avoidance, detoxification, or even capture of their hosts defensive chemicals. Harnessing and optimizing the chemical defense capabilities of crops has the potential to aid in the continuing struggle to enhance or improve agricultural pest management. Such strategies include breeding for the restoration of defense chemicals from ancestral varieties, or cross-species transfer of defense metabolite production.